Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals PDF

Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals Ross Piper Greenwood Press EXTRAORDINARY ANIMALS EXTRAORDINARY ANIMALS An Encyclopedia of Curious and Unusual Animals Ross Piper Illustrations by Mike Shanahan GREENWOOD PRESS Westport, Connecticut London Library of Congress Cataloging-in-Publication Data Piper, Ross. Extraordinary animals : an encyclopedia of curious and unusual animals / by Ross Piper ; Illustrations by Mike Shanahan. p. cm. ISBN-13: 978–0–313–33922–6 (alk. paper) ISBN-10: 0–313–33922–8 (alk. paper) 1. Animals—Encyclopedias. I. Title. QL7.P57 2007 590—dc22 2007018270 British Library Cataloguing in Publication Data is available. Copyright © 2007 by Ross Piper All rights reserved. No portion of this book may be reproduced, by any process or technique, without the express written consent of the publisher. Library of Congress Catalog Card Number: 2007018270 ISBN-13: 978–0–313–33922–6 ISBN-10: 0–313–33922–8 First published in 2007 Greenwood Press, 88 Post Road West, Westport, CT 06881 An imprint of Greenwood Publishing Group, Inc. www.greenwood.com Printed in the United States of America The paper used in this book complies with the Permanent Paper Standard issued by the National Information Standards Organization (Z39.48–1984). 10 9 8 7 6 5 4 3 2 1 In memory of my Dad CONTENTS Preface xi Acknowledgments xiii Introduction xv 1 Strength in Numbers: Animal Collectives 1 Acacia Ant 1 Antarctic Krill 4 Aphids 6 Giant Japanese Hornet 9 Leaf-Cutter Ants 11 Naked Mole Rat 13 New Zealand Bat-Fly 16 Portuguese Man-of-War 18 Sponges 20 Stony Corals 23 Tar-Baby Termite 25 Trap Ant 27 2 The World Is a Dangerous Place: Defensive Tactics 31 Armored Shrew 31 Balloon Fish 33 Bombardier Beetles 35 Bushy-Tailed Wood Rat 38 Electric Eel 40 Glaucus 42 Goliath Tarantula 44 Honey Badger 47 Hooded Pitohui 49 Mimic Octopus 51 viii CONTENTS Sea Cucumbers 53 Slow Loris 55 Springtails 58 3 The Quest for Food 61 Ant Lions 61 Aye-Aye 63 Bolas Spiders 66 Bulldog Bat 68 Candirú 70 Common Chameleon 72 Cone Shells 74 Cookie-Cutter Shark 76 Egg-Eating Snake 78 Fat Innkeeper 80 Gharial 83 Giant Anteater 85 Harpy Eagle 87 Kiwis 89 Luminous Gnat 92 Mantis Shrimps 94 Megamouth Shark 96 Portia Spider 98 Purse-Web Spider 100 Shrews 103 Spitting Spider 105 Triclads 107 Velvet Worms 109 4 Getting from A to B: Solutions to the Problem of Movement 113 Bee Hummingbird 113 Common Swift 115 Emperor Penguin 117 European Eel 119 Flying Dragons 122 Four-Wing Flying Fish 124 Grant’s Golden Mole 126 Leatherback Turtle 128 Northern Blueﬁn Tuna 130 Sea Lamprey 132 Sloths 135 Stenus Rove Beetles 137 Stowaway False Scorpion 139 Tokay Gecko 141 White Worm Lizard 144 5 Looking Out for the Next Generation 147 Bee Wolf 147 Blue Whale 149 Burying Beetles 152 Fig Wasps 154 King Cobra 156 CONTENTS ix Malleefowl 158 Marble Gall Wasp 161 Platypus 163 Red-and-Blue Poison-Arrow Frog 165 Sand Tiger Shark 168 Ship Timber Beetle 170 6 Living at the Expense of Others: Parasitism 173 Alcon Blue Butterﬂy 173 Ant-Decapitating Flies 175 Bird Fluke 178 Cod Worm 180 Cricket Fly 182 Giant Roundworm 184 Gordian Worms 187 Guinea Worm 189 Human Botﬂy 192 Leaf Wasps 194 Rabbit Flea 196 Red-Tailed Wasp 199 Sabre Wasp 201 Sacculina 204 Strepsipterans 206 Warble Flies 208 7 The Continuation of the Species: Sex and Reproduction 211 Blue-Headed Wrasse 211 Cockroach Wasp 213 Deep-Sea Angler Fish 215 Green Spoon Worm 218 Narwhal 220 Palolo Worms 222 Pocketbook Mussels 224 Spotted Hyena 226 Surinam Toad 228 Taita Hills Caecilian 231 Tarantula Hawks 233 Transvestite Rove Beetle 235 8 Pushing the Boundaries: Surviving Extremes 239 Antarctic Toothﬁsh 239 Beard Worms 241 Coconut Crab 244 Coelacanth 247 Giant Mudskipper 249 Giant Squid 252 Hagﬁsh 254 Human 256 Lake Titicaca Frog 259 Lungﬁsh 261 Marine Iguana 263 Olm 266 x CONTENTS Sperm Whale 268 Sun Spiders 270 Symbion 273 Water Bears 275 Water Spider 278 Zombie Worm 280 Glossary 283 Selected Bibliography 289 Index 291 PREFACE Extraordinary Animals is an exploration of the animal kingdom, a cherry-picking of these fantas- tically diverse organisms whose ways and characteristics are astounding and often stranger than ﬁction. The book covers a wide variety of animal life, including many obscure but exceptionally interesting creatures, the likes of which can only be discovered in the conﬁnes of specialized, very inaccessible textbooks. Not only is the diversity of the subject matter unique, but the content has been thoroughly researched for scientiﬁc accuracy and is written in a way that it is clear, engag- ing, and enthusiastic. The audience for Extraordinary Animals is basically anyone with an interest in nature—the sort of people who buy books from the natural history section of a bookstore or who enjoy nature documentaries. The main purpose of Extraordinary Animals is to highlight just how re- markable animals are in a way that just about anyone can read and understand. Textbooks are full of fascinating information, but all too often, they are inaccessible to general audiences. This book provides a bridge to those resources for anyone who has even the slightest interest in the natural world. In this book, you will ﬁnd 120 animals separated into one of eight categories. You can dip into the book wherever you want to as it is not laid out so that you have to read it from cover to cover. Each piece contains information on how the animal is classiﬁed, what it looks like, how big it is, and where it lives. The main body of the piece is devoted to the extraordinary natural history or characteristics of the animal. A number of bulleted facts give some extra, interesting information on the animal. Some of the animals in the book can quite easily be found in a back- yard or in places that are not that exotic, and in these cases, there is a “Go Look!” section that gives tips on how and where to ﬁnd them, how to watch them, and how to look after them in captivity for short periods of time. It was the initial intention to include a list of Web sites to which the reader could go to ﬁnd additional information on these animals; however, the content of these sites can never be guar- anteed, and with the constant reshuﬄing of pages on the Web, links can rapidly become inactive xii PREFACE or useless. For those readers keen to trawl the Web for extra information, the best way is to type the Latin name, or perhaps the common name, into an Internet search engine. The amount of information on the Web today is such that there will be numerous pages on most of the animals in this book, but only those sites ending in.gov or.edu will carry information that has been thor- oughly researched and edited. At the end of many entries, there is a list of resources for further reading. These lists, as well as the selected bibliography at the end of the book, include textbooks and journal articles that can be found in any decent library. Some of these books have an asterisk (*) appearing next to them—it is these resources that I heartily recommend you buy as they are a treasure trove of information for anyone interested in the natural world. Wherever possible, I have tried not to use jargon. There is a whole dictionary of specialized zoological terms, which can sometimes be confusing or diﬃcult to say. I have tried to write in more general terms without using this specialized language. However, there is a glossary at the end of the book to explain any jargon that was unavoidable. ACKNOWLEDGMENTS I would like to thank the following individuals for their comments and suggestions on earlier versions of the manuscript: John Alcock, Christian Bordereau, Tom Buckelew, Jason Chapman, Steve Compton, Paul Cziko, Ian Denholm, Stephanie Dloniak, Jack Dumbacher, Mark Eber- hard, Howard Frank, Megan Frederickson, Douglas Fudge, Ram Gal, Mike Howell, Robert Jackson, Jeﬀ Jeﬀords, David Julian, Uwe Kils, Alex Kupfer, Jim Macguire, Andrew Mason, David Merritt, William Miller, Claudia Mills, Sarah Munks, Phil Myers, Dick Neves, Arne Nilssen, Jerome Orivel, Robert Presser, Galen Rathbun, Thomas Roedl, Ernest Seamark, Andrei Soura- kov, Erhard Strohm, Paul Sunnucks, Laurie Vitt, Ashley Ward, Marius Wasbauer, and Philip Weinstein. I would also like to thank Mike Shanahan for his brilliant illustrations, Lucy Siveter of Image Quest Marine for sourcing images, Adam Simmons for reviewing an early draft of the manuscript, and Roger Key. I would like to thank Bart Hazes and Mike Howell for going out of their way to help me. Special thanks go to Kevin Downing for giving me the chance to write this book. INTRODUCTION The earth, from a purely celestial point of view, is unremarkable. It is a small planet in a solar system orbiting a medium-sized star in a smallish galaxy, the Milky Way, which contains billions of solar systems. The Milky Way is but one of billions upon billions of galaxies in the incompre- hensible vastness of the universe. Yet, in one respect, the earth is special beyond compare. It is the only place we know of on which there is life. Life is such a small, seemingly insigniﬁcant word, yet it encompasses a fantastic diversity of living forms. The exact time and nature of life’s appearance on the earth has divided scientists for decades, and it will continue to do so because the time spans with which we are dealing are huge, almost impossible for us to grasp, and the evidence is fragmentary and hard to come by. What we do know is that the earth is very, very old—4.6 billion years old to be exact—but for the vast majority of this time, it was a lifeless globe cooling from the ﬁres of its creation, circling the sun in the young solar system, while being heavily bombarded by asteroids. Over hundreds of millions of years, the earth changed and the asteroid impacts became less frequent. Oceans formed and our planet became slightly more hospitable, but conditions on this primor- dial Earth were still very diﬀerent from the comparatively balmy conditions we enjoy today. And then, more than 3 billion years ago, the ﬁrst life evolved. Where and how are questions we can only make good educated guesses at, but an experiment conducted in the 1950s by scientists in the United States showed that lightning bolts discharged through an atmosphere, the likes of which could have shrouded the young Earth, could have produced biological molecules—the precursors of the ﬁrst simple cells. Although these experiments have since been called into ques- tion, as more recent ﬁndings suggest that the mix of gases used by the scientists to mimic the atmosphere of the young earth was probably inaccurate, they do give us an idea of what may have happened all those millions of years ago. The complexity of these ﬁrst biological molecules increased over the eons, eventually forming the ﬁrst self-contained biological systems, which in turn gave rise to the ﬁrst proper cells—the ﬁrst life. xvi INTRODUCTION This ﬁrst life was no more than simple, single-celled organisms, and these organisms had the earth to themselves for a long, long time. In the atmosphere that shrouded the earth at this time, oxygen was as good as absent, but it is thought these ﬁrst life-forms created oxygen as a waste gas. Over more immense stretches of time, the levels of oxygen in the atmosphere steadily grew until oxygen became quite abundant. Then, around 700 million years ago, this simple life gave rise to increasingly complex forms. From that point onward, the diversity of life on earth exploded. Lots of diﬀerent life-forms and body plans appeared, some of which were success- ful, spawning long, unbroken lines of descent, while others disappeared into prehistory. The life-forms interacted with and adapted to each other, becoming ever-more entwined. The ex- traordinary diversity of life on earth today reﬂects the relationship between organisms and their environment—an intricate web of interactions with the continual processes of adaptation and change, ﬁne-tuning every species over time to its environment. Life-forms have become so at- tuned to their environment that scarcely a niche is vacant; in almost every conceivable habitat on earth, animals can be found. In the deepest parts of the ocean, more alien to us than the surface of Mars, creatures thrive. Even in the coldest and highest places on earth, you would be hard pressed not to see some form of animal life. To us, perhaps the most bizarre place to live is inside another animal, yet many creatures have taken to this parasitic way of life and have become very good at it. Traditionally, scientists have classiﬁed life on earth into ﬁve diﬀerent kingdoms based primar- ily on shared characteristics. This system has undergone many modiﬁcations, but it is straight- forward and I use it in this book to describe how animal life is categorized. This system of classiﬁcation is hierarchical, starting with the kindgom level, followed by phylum, class, order, family, genus, and species. Organisms are named by a two-word system, the genus followed by the speciﬁc epithet, which together give the species’ scientiﬁc name. For example, the European honeybee’s scientiﬁc name is Apis (genus) mellifera (speciﬁc epithet). In this classiﬁcation scheme, the ﬁrst and most primitive kingdom is that of bacteria. Next are the plants, familiar to us as they dominate terrestrial ecosystems. The fungi represent the third kingdom. The fourth kingdom is the one to which we belong—the animals. The ﬁfth kingdom, a sort of taxonomic dustbin, in- cludes the protists, organisms that do not really ﬁt in to any of the other four kingdoms. The topic of this book is the diversity of the animal kingdom, but you will not ﬁnd an inex- haustible list of all of the animals on earth between the covers of this book—far from it. Such a book would take years to read, and it would hardly be the sort of thing you could easily keep on your bookshelf. No, this is essentially a cherry-picking of the animal kingdom. It only covers living animals because although long extinct animals are fascinating, their lives are the stuﬀ of guesstimation. Bones and impressions of long dead bodies can only tell so much. This book is a selection of those animals whose fantastic habits and lives really hammer home the message of how remarkable our planet is. All the animals you will read about are real. Some are found out- side your back door; others dwell in habitats where humans rarely venture. Some are miniscule, barely visible to naked eye, and some are massive, thousands of times larger than a fully grown human. Many of them are rarely seen, and there is still a great deal to learn about their lives. The scientists who study animals are known as zoologists, and it is these people who unravel the mysteries of the animal kingdom. Scientists, by their very nature, have an urge to catego- rize and order the things they study, and zoologists are no exception. All animal life may be divided into 38 diﬀerent categories, or phyla. Each phylum contains animals that in one way or another are very similar, and they may be grouped by shared physical characteristics or genetic INTRODUCTION xvii similarities. Animals are continually being shifted within and between these phyla as scientists understand more about DNA and genetics. It has to be remembered that these phyla are a con- struct of the human mind and are merely an abstraction that allows us to make sense of the natural world. The number of species within these phyla is a huge bone of contention. Estimates range from 1.5 million to 100 million, but we may never know the true number. Regardless of the human need to categorize and identify things, it goes without saying that animals are a source of intense interest for a large percentage of the population. Perhaps this stems from the more primitive days of the human race when we lived in much greater harmony with nature. Before the days of agriculture and even civilization, our forebears would not have lasted long without a thorough understanding of the animals that shared their environment— which species they could use for food and which species they should avoid. Today, you can still see this impressive level of understanding in the ways of the tribes that survive in the more re- mote reaches of our planet. For thousands of years, aboriginal people have lived in the same way thanks to their intimate knowledge of the world about them. Today, most people’s interest in animals begins in childhood with the creatures found in a typical backyard, inevitably, the ones lovingly described as creepy-crawlies—the insects and their relatives. These animals are easy to ﬁnd and easy to keep in glass jars or old margarine tubs. This fascination with bugs grows, and before long, you ﬁnd yourself reading about other animals, some of which you will probably never see but whose origins, diversity, and astonishing lives amaze you. This book is an encapsulation of this path of curiosity, and it draws on things I have read and things I have seen. I hope that whoever reads this will ﬁnd the animals contained herein as interesting as I do. 1 STRENGTH IN NUMBERS: ANIMAL COLLECTIVES ACACIA ANT Acacia Ant—The ant on the acacia tree on which it lives. (Mike Shanahan) 2 EXTRAORDINARY ANIMALS Scientiﬁc name: Pseudomyrmex ferruginea Scientiﬁc classiﬁcation: Phylum: Arthropoda Class: Insecta Order: Hymenoptera Family: Formicidae What does it look like? This ant is a slim-bodied species, with the workers measuring around 3 mm in length. They are orangey brown and have very large eyes. Where does it live? This is an arboreal ant, and it is to be found on or around a certain species of acacia tree that is found throughout Central America. The ants nest inside the large thorns of these acacias. A Relationship among the Thorns Acacia trees with their succulent little leaves are relished by a large number of herbivorous animals from tiny insects to huge mammals. To protect their foliage from these hungry mouths, they have evolved a number of ways to keep the leaf eaters at bay. Many acacias have vicious-looking spines, while others have leaves packed with repellent and noxious chemicals. Some acacias, however, have gone even further and actually depend on other animals for pro- tection. One such acacia, the bull’s horn acacia, has its own species of dedicated ant bodyguard. The relationship begins when a young queen ant, newly mated, lands on the acacia looking for a place to start a nest. The thorns on this acacia are great little ant havens as they are bulbous at their base and hollow. The queen, convinced by the odor of the tree that she is in the right place, starts to nibble a hole in the tip of one of the thorns, eventually breaking through to the cavity within. In the safety of her new nest she lays 15–20 eggs, and soon enough, these give rise to the ﬁrst generation of workers. The embryonic colony grows, and as it does, it expands into more of the bulbous thorns. When the colony has exceeded around 400 individuals, the repayment to the acacia for lodgings can begin, and the ants assume their plant-guarding role. The ants become aggressive and do not take kindly to any creature they ﬁnd trying to sur- reptitiously munch the acacia’s leaves, regardless of whether it is a cricket or a goat. It doesn’t take much to set them oﬀ. Even the whiﬀ of an unfamiliar odor sees the ants swarming from their thorns and toward a potential threat. Herbivorous insects are killed or chased away, and browsing mammals are stung in an around their mouth, which quickly persuades them to look elsewhere for less well-defended fodder. Apart from these active defending duties, the ants also have gardening to tend to—they leave the tree and scout around its base looking for any seed- lings that would eventually compete with their acacia for light, nutrients, and water. If they do ﬁnd any, they destroy them, and the ants even go so far as to prune the leaves of nearby trees so that their host is not shaded out. Not only does the tree supply the ants with nesting sites, but special glands at the base of the tree’s leaves produce a nectar rich in sugars and amino acids that the ants lap up. The tips of the leaves also sprout small, nutritious packets of oils and proteins (Beltian bodies), which the ants snip oﬀ and carry away to feed to their grubs. The grubs even have a little pouch at their head end which the Beltian body can be tucked into while they feast on it. This charming relationship between the ants and the acacias is as not as wholesome as it ﬁrst appears. The ants will repel most herbivorous insects, but they turn a blind compound eye to STRENGTH IN NUMBERS 3 the feeding antics of scale insects, which suck the sap of the host acacia, thus weakening it and providing entry for disease. The ants tolerate and even protect the scale insects because they produce sweet honeydew, which the ants relish. This is not the only example of a symbiotic relationship between a tree and an ant species. There are at least 100 species of ants that live in a close partnership with a plant. In return for the services provided by the ants, the plants furnish them with accommodation. The diversity of the relationships encompasses all the conceivable parts of a plant. Some plants have modiﬁed swellings on their branches and twigs, while others have cavities within their stems and trunks or modiﬁed roots that house their insect guests. Some of these nests can be very small, only a few centimeters across, while others can be large and elaborate. In South America, there is a tree, Duroia hirsute, which is sometimes found to domi- nate small areas of the rain forest, forming areas that the local people call “devil’s gardens.” Within special cavities on the tree’s trunk there are special cavities in which the ant, Myrmelachista schumanni, makes its nest. Any saplings sprouting near the host tree are attacked by the ants and stung with formic acid, which kills them, thus removing competition for their host’s resources. In some of these relationships, the cost of the ant’s protection can be quite expensive. Cordia trees in the Amazonian rain forest have a kind of partnership with Allomerus ants, which make their nests in modiﬁed leaves. To increase the amount of living space available to them, the ants will destroy the tree’s ﬂower buds. The ﬂowers die and leaves develop instead, providing the ants with more dwellings. Another type of Allomerus ant lives with the Hirtella tree in the same forests, but in this relationship, the tree has turned the tables on the greedy ants. When the tree is ready to produce ﬂowers, the ant abodes on certain branches begin to wither and shrink, forcing the occupants to ﬂee and leaving the tree’s ﬂowers to develop free from attack by the ants. In the mangrove forests of Southeast Asia and New Guinea there lives an odd plant called Myrmecodia. This green, spiky, small football-sized plant clings to the branch or trunk of a mangrove tree. Scuttling over its surface are numerous ants, and the odd plant is their home. Open it and an elaborate system of tunnels and chambers will be revealed. Some of these chambers are the nest’s rubbish tips, and the waste therein is used by the plant as a fertilizer, allowing it to ﬂourish even though its roots will never come into contact with the soil. As you can see, ants have struck up some amazingly complex relationships with plants. On the whole, the two very diﬀerent organisms help each other, but occasion- ally, there are freeloaders. These stories exemplify the degree to which insects and ﬂowering plants have become inextricably linked over millions of years. Ever since the ﬂowering plants ﬁrst appeared on earth many millions of years ago, the insects have gravitated toward them and evolved with them, resulting in the complex relationships we see today. Further Reading: Frederickson, M., Greene, M. J., and Gordon, D. M. “Devil’s gardens” bedevilled by ants. Nature 437, (2005) 495–96. 4 EXTRAORDINARY ANIMALS ANTARCTIC KRILL Antarctic Krill—A whale moving in to engulf a Antarctic Krill—An adult krill clearly showing the swarm of Antarctic krill. (Mike Shanahan) feeding basket formed by its forelimbs. (Uwe Kils) Scientiﬁc name: Euphausia superba Scientiﬁc classiﬁcation: Phylum: Arthropoda Class: Malacostrata Order: Euphausiacea Family: Euphausiidae What does it look like? The Antarctic krill can be about 6 cm long when fully grown, and it is more or less transparent, with a pair of big black eyes. The antennae are long and sprout from the very front of the head. The thorax bears several pairs of specialized limbs that form a basketlike structure. The abdomen has several pairs of swimming limbs and ends in a paddle called the telson. Where does it live? This crustacean is found in the southern waters surrounding the con- tinent of Antarctica. Their preferred habitat varies depending on how old they are. As youngsters, they dwell at great depths, but young adults and adults spend their time in surface waters. Swarming Crustaceans There can be few animals whose importance in the planet’s ecosystems is as great as the Antarctic krill. Singly, they are not that impressive. They look like a myriad of other shrimplike animals, but what they lack in appearance they more than make up for in sheer abundance. The life of an Ant- arctic krill starts as a fertilized egg, about the size of a period, sinking into the abyss. As the egg descends, its cells divide and diﬀerentiate to form the young larva. At a depth of between 2,000 and 3,000 m, the baby krill hatches and begins to ascend, developing and growing as it makes slow but steady progress through the icy waters, sustained by the remaining yolk from its egg. STRENGTH IN NUMBERS 5 In the surface waters, the young krill that have made their way successfully from the depths begin to form huge groups, known as swarms. The individuals in these groups continue growing, and it can take between two and three years from the time they hatch for them to reach maturity. The swarms are composed of adults and young adults and can be huge. They can stretch over an area of ocean equivalent to several city blocks and can be as much as 5 m thick, with as many as 60,000 krill in 1 cu. m of water. From the air, one of these swarms has been likened to a gigantic amoeba as it moves slowly through the water, changing shape as it goes. The preferred food of krill are the tiny, single-celled plantlike organisms called diatoms. These diatoms rely on the sun’s rays for energy, using the power of sunlight to convert carbon dioxide and water into simple sugars—the all-important process of photosynthesis. As they are sun worshippers, these diatoms are only found in surface waters. They are found in such huge numbers that they form a kind of soup along with other minute organisms. These diatoms not only ﬂoat freely in the water but also coat the underside of the pack ice, forming verdant lawns. The krill graze these upside-down pastures like tiny, multilimbed cows and also swim through the plankton using their front limbs like a straining basket to separate the edible cells from the water. They scrape these appendages clean with their mouthparts and swallow the green paste. They are messy eaters, and a lot of the green globules miss the crustaceans’ mouths and sink slowly to the seaﬂoor. The digestive system of krill is also far from eﬃcient, and quite a large proportion of what they take in is egested without being broken down. These strings of krill waste follow the feeding debris to the sea bottom. All of this accumulating waste is known as a so-called biological pump, as an incomprehensible amount of atmospheric carbon dioxide, utilized by the diatoms, is locked away on the seaﬂoor for around 1,000 years. This process is massively important in the regulation of the earth’s climate. Today we are seeing the conse- quences of too much carbon dioxide in the atmosphere. Just suppose that for some unknown reason these delicate little animals were to disappear from the face of the earth tomorrow. If they were inexplicably whisked away, we would not only see the collapse of marine ecosystems everywhere, as they are eaten by so many other animals, but also the full and relentless fury of runaway global warming. There are around 86 species of what can be described as krill. Regardless of the species, they are all considered keystone species in marine ecosystems. They occur in such huge numbers that many animals depend solely on them for food. The huge cetaceans, like the blue whale, are a good example. Their diet consists of krill and whatever else happens to be swimming among the swarm. The total mass of Antarctic krill in the ocean during the peak of the season is esti- mated to be on the order of 125–725 million tonnes, making this species probably the most successful animal on the planet, in terms of biomass at any rate. For reasons that are not fully understood, krill numbers go through cyclical peaks and troughs that are thought to be linked to the abundance of pack ice surrounding Antarctica. In years where there is lots of pack ice, it provides numerous little nooks, crannies, and caverns in which the young krill can shelter from their many predators. They appear to suﬀer when there is little pack ice. In these lean years, they are replaced as the dominant plankton animal by jelly-bodied creatures called salps. In some areas of the Southern Ocean there are unusual places rich in nutrients, but where the diatoms and other photosynthesizing, single-celled organisms are 6 EXTRAORDINARY ANIMALS surprisingly rare. As there is no food for them, the krill are absent from these areas. It turns out that these odd tracts of ocean lack iron. Injecting iron gives the plantlike organisms what they need, and before long they bloom, attracting the attention of the gigantic swarms of krill. It has been suggested that ships could circle the Southern Ocean and inject iron into the water. This would stimulate the diatom populations and, in turn, the krill, providing a way of engineering the environment to increase the amount of carbon dioxide that is locked away in the deep ocean. Around 100,000 tonnes of this Antarctic krill species, Euphausia superba, is taken every year for animal and human consumption. In Japan, processed krill is known as okiami. The Antarctic krill, like all its relatives, sheds its skin very regularly. It is peculiar not only for the speed with which it can do this but also for its ability to grow smaller at each successive molt if food is scarce. The Antarctic krill can quite literally jump out of its old skin, leaving the skin ﬂoating in the water, where it may act as decoy to confuse predators. Further Reading: Everson, I. Krill: Biology, Ecology and Fisheries. Blackwell Science, Oxford 2000; Hamner, W. M., Hamner, P. P., Strand, S. W., and Gilmer, R. W. Behavior of Antarctic krill, Euphausia superba: chemoreception, feeding, schooling and molting. Science 220, (1983) 433–35; Loeb, V., Siegel, V., Holm-Hansen, O., Hewitt, R., and Fraser, W. Effects of sea-ice extent and krill or salp dominance on the Antarctic food web. Nature 387, (1997) 897–900; Ross, R. M., and Quetin, L. B. How productive are Antarctic krill? BioScience 36, (1986) 264–69. APHIDS Scientiﬁc name: Aphids Scientiﬁc classiﬁcation: Phylum: Arthropoda Class: Insecta Order: Homoptera Family: Aphididae What do they look like? Aphids are small insects, varying in size from 1 to 10 mm. They have soft bodies with long, spindly legs. There is normally a pair of thin turrets projecting from the animal’s back end, which secrete a waxy substance. In each species there are winged and nonwinged forms. The mouthparts are formed into a long, thin structure called the rostrum, which is held under the body when the animal is not feeding. The eyes are small and rela- tively simple compared to other insects. Where do they live? Aphids are found worldwide, but they are more common in temperate regions. They are found on a quarter of all plant species. Aphids, Aphids Everywhere Aphids are not held in high regard. The damage they do to plants has made them enemies of gardeners and farmers the world over. From a purely zoological point of view, however, they are a fascinating and very successful group of animals. One of the most remarkable things about aphids is their reproductive ability. In a short amount of time, a plant free from aphids can be swarming with them. For much of the year, many species of aphids reproduce without mating. STRENGTH IN NUMBERS 7 Aphids—A female aphid giving birth to a clone of herself. (Mike Shanahan) This cycle begins with a female that hatches from an egg laid in a suitably secluded spot, such as the deep ﬁssures in tree bark, during the previous year. This founding female had a mother and a father, but due to the odd make up of the aphid’s chromosomes, a mating between a male and female can only ever produce daughters. These daughters survive the winter, and within them, they carry the seed of the new population. The founding female is already carrying a daughter, and within this embryo, another embryo develops—three generations in the body of one small animal, all thanks to the phenomenon of parthenogenesis, which enables animals to reproduce without sex. These daughters are born as miniature replicas of their mother, and they, too, give birth to further replicas, until there are huge numbers of aphids—all originating from the original female that survived the winter as an egg. The reproductive capacity of aphids is astounding. Theoretically, if all of the oﬀspring from a single cabbage aphid managed to survive, there would be 1.5 billion, billion, billion aphids by the end of the season. During the autumn, the aphid colony will start producing males and females whose function it is to mate and produce the founding females for the following year. In certain species of aphids, some of the clones, although genetically identically to the original female, will look slightly diﬀer- ent and perform certain tasks, such as guarding the colony. These castes are commonly soldiers with enlarged front legs and a spiky head, which is jabbed at animals threatening the colony. During the feeding season, the aphid colony may become too big, resulting in overcrowding that may kill the host plant. In these situations, the aphids start giving birth to winged individuals. These alates, as they are known, will leave the colony to search for new food plants. There are more than 4,000 species of aphids, and they are believed to have appeared more than 280 million years ago when there were far fewer plant species than there are today. Around 100 million years ago, there was an explosion in the variety of ﬂowering plants, and the aphids diversiﬁed to exploit this new abundance of plant 8 EXTRAORDINARY ANIMALS species. Over the eons, the aphids, as with many of the insects, have evolved Go Look! hand in hand with the ﬂowering plants, Aphids can be found on all types of plants, including resulting in some amazingly complex houseplants, garden plants, trees, and crops. You will see a relationships. whole array of interesting behaviors if you watch a colony of Aphids live in colonies, and in some aphids. Typically, a colony will feed on the plant with their mouthparts inserted into the plant, greedily sucking the species, certain individuals have a plant’s sap. If you look carefully, you may see some of the speciﬁc task to fulﬁll, such as guarding females giving birth to miniature replicas of themselves. If the colony. The only other insects to live the colony is really crowded, winged aphids will be testing in colonies where all of the individuals their wings, hoping to ﬂy away in search of new host plants. are very closely related to one another On the same plant, ants could be tending the aphids, wait- and where the colony members are ing patiently at the animals’ rear ends for drops of sweet honeydew to appear. To encourage the aphids to produce divided into castes are the ants, wasps, some honeydew, the ants stroke the aphids with their an- bees, and termites. tennae. Stalking the aphids may be a range of predatory All aphids use their piercing, strawlike insects, including adult ladybirds and their active larvae, mouthparts to penetrate the phloem and lacewings and their fearsome looking larvae with huge vessels of their food plant. These vessels sickle-shaped mandibles. Small maggots also hunt the aphids. These are the larval stage of hoverﬂies, a common transport nutrients, as sap, to all parts sight on ﬂowers. You may notice small ﬂying insects buzz- of the plant, and the aphids gain access ing around the aphids; these are female parasitic wasps. to these tubes through the leaves, stem, Watch a wasp carefully, and you will see it approach an or roots. As the aphid inserts its feeding aphid, touching it all over with her long antenna to “smell” straw into the plant, the tip produces a whether it has already been parasitized before carefully in- ﬂuid that hardens, forming a tube. To jecting an egg into the sap sucker’s soft body. enter the phloem, the aphid must slowly rupture the plant cells, and to prevent the hole from healing, the aphid produces special proteins that fool the plant’s defense mechanisms. It can take a long time for the aphid to get its ﬁrst sip of the plant’s ﬂuids—anywhere between 25 minutes and 24 hours. To help digest the plant ﬂuids, aphids enlist the services of bacteria or yeast. These microorganisms are present in the gut of the insect and feed on the sap, producing nutrients vital to the aphid. This is an example of symbiosis. Much of what the aphid sucks from the plant is little more than sugary water, and so to stop from inﬂating itself with liquid, the aphid must get rid of the excess ﬂuid as it is feeding. Droplets of sugary ﬂuid, a substance that is commonly known as honeydew, emerge from the aphid’s back end. Many animals have a special taste for this sugary treat, none more so than ants. Ants like honeydew so much that they treat the aphids like cows: herding them, protecting them, and milking them. This mutually beneﬁcial arrangement is another reason why aphids are so successful. Many of the animals that would feed on them are deterred by the presence of their ant guardians. Aphids don’t get everything their own way. Although they have ants as minders, paid with honeydew, there are many animals, especially other insects, that feed on aphids or parasitize them. The ladybirds are one such example, as both the larval and adult stages of these beetles eat huge numbers of aphids. Many parasitic wasps hunt aphids, inject- ing eggs into their soft little bodies. These eggs hatch into small grubs and feed on the aphids’ internal organs, eventually killing them. STRENGTH IN NUMBERS 9 Plants lose many vital nutrients to aphids, which may explain the evolution of vari- ous defense mechanisms to discourage the aphids from feeding, such as small spines, hairs, scales, and secretions on all parts of the plant. Aphids are not strong ﬂiers, but they utilize lofty air currents to travel many kilometers, often ﬂying up to reach these currents in the calm conditions of a summer evening. GIANT JAPANESE HORNET Giant Japanese Hornet—Japanese honeybee work- Giant Japanese Hornet—A worker perched on ers forming a defensive ball around a giant Japanese an index finger to give an idea of scale. (Takehiko hornet. (Mike Shanahan) Kusama) Scientiﬁc name: Vespa mandarinia japonica Scientiﬁc classiﬁcation: Phylum: Arthropoda Class: Insecta Order: Hymenoptera Family: Vespidae What does it look like? The giant Japanese hornet is a large insect. The adult can be more than 4 cm long with a wingspan of greater than 6 cm. It has a large yellow head with large eyes, a dark brown thorax, and an abdomen banded in brown and yellow. Three small simple eyes on the top of the head can be easily seen between the large compound eyes. Where does it live? This subspecies of the Asian hornet is found on the Japanese islands. They prefer forested areas where they make their nests in tree holes. Marauding, Hive-Raiding Hornets Japanese beekeepers, in an attempt to increase productivity, try to keep European honeybees in Japan as they produce more honey than the indigenous Japanese honeybees. However, the giant Japanese hornet often thwarts this enterprise. This hornet is a formidable brute of an insect, which is in fact one of the largest living wasps. When a hornet locates a hive of European honeybees, it leaves a pheromone marker all around the nest, and before long, its nest mates pick up the scent and converge on the beehive. The hornets ﬂy into the beehive and begin a systematic massacre. The European honeybee is no match for the hornet as it is one-ﬁfth the size. A single 10 EXTRAORDINARY ANIMALS hornet can kill 40 European honeybees in one minute, and a group of 30 hornets can kill a whole hive, something on the order of 30,000 bees, in a little over three hours. The defenseless residents of the hive aren’t just killed but are horribly dismembered. After one of these attacks, the hive is littered with disembodied heads and limbs as the hornets carry the thoraxes of the bees back to their own nest to feed their ravenous larvae. Before they leave, the hornets also gorge themselves on the bees’ store of honey. This amazing natural phenomenon begs the question, well what about the native Japanese honeybees? Do they get attacked? The answer is no, and the reason is particularly neat. The hornet will approach the hive of the Japanese honeybee and attempt to leave a pheromone marker. The Japanese honeybees sense this and emerge from their hive in an angry cloud. The worker bees form a tight ball, which may contain 500 individuals, around the marauding hornet. This defen- sive ball, with the hornet at its center, gets hot, aided by not only the bees vibrating their wing muscles but also by a chemical they produce. The hornet, unlike the bees, cannot tolerate the high temperature, and before long, it dies and the location of the Japanese honeybees’ nest dies with it. Aside from its large size and fearsome appearance, the giant Japanese hornet also has very potent venom, which is injected through a 6.25 mm stinger. The venom attacks the nervous system and the tissues of its victim, resulting in localized tissue damage where the ﬂesh is actually broken down. A sting from this insect requires hospital treatment, and on average, 40 people are killed every year after being stung by giant hornets, due to anaphylactic shock. Typically, the hornets are not aggressive animals, but when threatened, they will attack. An attack initially involves one individual, but the release of alarm pheromones will quickly attract its sisters. Not only is the venom dangerous, but the sting is also very painful. A Japanese entomologist said of the sting: “It was like a hot nail through my leg.” Hornet workers continually forage to feed their siblings developing in the nest. They will take a range of insects, including crop pests, and for this reason, they are con- sidered beneﬁcial. The insects they catch are dismembered, and typically, the most nutritious parts, such as the ﬂight muscles, are taken back to the nest where they are chewed into a paste before being given to a larva. The larva returns the favor by producing a ﬂuid that the worker eagerly drinks. The ﬂuid produced by hornet larvae has aroused interest recently as it is the only sustenance the adult worker imbibes during its life. This substance somehow makes prodigious feats of stamina possible, as worker hornets ﬂy for at least 100 km a day at speeds of up to 40 km/h. The substance produced by the hornet larvae, known as vespa amino acid mixture (VAAM), somehow enables intense muscular activity over extended periods, perhaps by allowing the increased metabolism of fats. A company has started producing VAAM commercially, and it has apparently improved the per- formance of many athletes. Not only is VAAM popular amongst the Japanese athletic community, but the fully grown larvae of the hornet are considered something of a delicacy and are eaten in mountain villages, either deep-fried or as hornet sashimi. The defensive-ball strategy of the Japanese honeybee works because the tempera- ture inside the ball rises to 47°C, and the lethal temperature for the giant hornet is 44°C–46°C, whereas the lethal temperature for the bee is 48°C–50°C. STRENGTH IN NUMBERS 11 Recent studies have shown that the brains of the Japanese honeybee workers responsible for attacking a scout giant hornet are infected with viruslike particles. It is thought that the infection triggers aggressive behavior in worker bees. More experiments are being carried out in an attempt to understand this interaction. Further Reading: Demura, S. Effect of amino acid mixture intake on physiological responses and rating of perceived exertion during cycling exercise. Perception and Motor Skills 96, (2003) 883–95; Ono, M., Igarashi, T., Ohno, E., and Sasaki, M. Unusual thermal defence by a honeybee against mass attack by hornets. Nature 377, (1995) 334–36; Tsuchita, H. Effects of a vespa amino acid mixture identical to hornet larval saliva on the blood biochemical indices of running rats. Nutrition Research 17, (1997) 999–1012. LEAF-CUTTER ANTS Leaf-Cutter Ants—A leaf-cutter ant worker carrying a cut section of leaf back to the nest. (Mike Shanahan) Scientiﬁc name: Atta and Acromyrmex species Scientiﬁc classiﬁcation: Phylum: Arthropoda Class: Insecta Order: Hymenoptera Family: Formicidae What do they look like? Within a single nest of leaf-cutter ants there are several types of workers, which vary in appearance. Generally, a leaf-cutter ant is brown, and its body supported on long, thin legs. The mandibles are well developed, and the eyes are small. 12 EXTRAORDINARY ANIMALS Where do they live? The leaf-cutter ants are found in Central and South America and in the southern United States. They like a warm, humid climate and throughout their range are found wherever there is suﬃcient vegetation to allow them to maintain a colony. Six-Legged Farmers Leaf-cutter ants form the largest and most complex animal societies on Earth. The workers in each nest are divided into several castes, all of which have a speciﬁc job to do. A colony of leaf-cutter ants is founded by a single female, the queen. This queen would have begun her life in another nest, tended and lavished with care by innumerable workers until the day she was ready to leave. The would-be queen crawls from the underground chambers of the nest into the open air. All around her there are other potential queens and males obeying with unerring synchronicity their reproductive instincts. The winged females and males take to the air for the ﬁrst and only time in their lives where they meet each other in ﬂight to mate. During this nuptial ﬂight (the revoada), the female mates with perhaps eight diﬀerent males to collect the 300 million sperm she needs to set up a colony. With her sperm bulbs full, she descends to the ground and rummages through the vegetation and leaf litter to ﬁnd a suitable crevice or hole that she can call home. She has no further need of her wings, so they fall oﬀ, easing her underground activities. Safely beneath the ground, the queen excavates a small chamber and uses a small scrap of fungus carried in a pouch beneath her chin to grow a fungus garden. The fungus is integral to the success of the colony, and the queen took a small piece from her birth nest. She does not eat this nutritious fungus but relies instead on body fat and her now useless wing muscles for sustenance. She starts laying eggs, and the ﬁrst young ants to hatch, her ﬁrst daughters, will be gardener-nurses. Their responsibilities are to look after the fungus garden and lovingly tend further eggs produced by the queen. These ﬁrst workers collect leaves from plants on the surface, on which the fungus grows. The queen, now relieved of menial tasks, can apply herself to the important job of enlarging the colony by pumping out eggs in huge numbers, producing diﬀerent types of workers to look after diﬀerent jobs within the nest. Some of the eggs will develop into nest generalists that will undertake all manner of miscellaneous tasks in the nest, while others will become foragers and excavators, col- lecting leaves for the fungus gardens and enlarging and maintaining the nest. Some eggs develop into heavy-headed workers with huge jaws whose job it is to defend the colony. After a few years, the nest, founded by a single female, has grown to monstrous proportions. It may descend 6 m underground, with a central nest mound more than 30 m across and smaller mounds extending out to a radius of 80 m. A single nest can take up 30–600 sq. m and contain 8 million individuals at any one time. One of these huge colonies operates like a superorganism, aﬀecting the sur- rounding environment in profound ways. The ants can completely defoliate whole areas of for- est, breaking the forest up into small glades that are important to many plants and animals. In the lifetime of one nest, 40 tonnes of soil can be turned over and aerated and fertilized by the huge amount of waste produced by the colony. This amazing collective of tiny insects working as one is all started by a single female that in her 10–15 year life span may produce 150 million daughters! There are approximately 38 species of leaf-cutter ants. During their nuptial ﬂights, potential queens can ﬂy more than 11 km from their birth nest. STRENGTH IN NUMBERS 13 The complex society of a leaf-cutter ant nest is held together by pheromones produced by the queen and built-in instincts. All the ants in a nest of leaf-cutters are sisters, and it is therefore in the interest of every individual to pull together for the sake of the colony. Everything that takes place in an ant nest is for the good of the colony, so that more would-be queens can be produced to carry the colony’s genes into the future. When a queen is spent and dies, the colony will lose its driving force and soon falter and collapse. When the colony is young, the queen will produce mostly smaller workers, but as the colony matures, the size of the workers will increase. Scientists have found that it is possible to deceive the queen of a mature colony into perceiving that she is in charge of a young nest. This was done by removing ants from the nest, reducing its size. Leaf-cutter ants are one of the only animals apart from humans to farm another organism. The crop in question is the fungus, and whatever its origins, it has devel- oped in such a close relationship with the ants that it is found only in their nests. When a cut section of leaf ﬁnds its way to the fungus chambers, the gardener ants will deposit a small drop of ﬂuid from their abdomen on the leaf with a tiny piece of fungus. The ant’s secretion acts like a form of fertilizer, allowing the fungus to proliferate through the leaf. The fungus gardens are prone to a bacterial disease, which can spell disaster for the ant colony. To stop this bacterial infection in its tracks, the ants can produce a potent antibiotic, which is applied to the gardens in much the same way as farmers apply pesticides to their crops. Starting a colony is a diﬃcult business, and only 2.5 percent of potential queens will be successful. Many will be eaten during the nuptial ﬂight or when they land, and many may successfully start a colony only to lose it to disease in the ﬁrst three months. In some parts of their range, leaf-cutter ants can be quite a nuisance to humans, defoliating crops and damaging roads and crops with their nest-making antics. Further Reading: Fowler, H., and Robinson, S. Foraging by Atta sexdens (Formicidae: Attini): seasonal pattern, caste, and efficiency. Ecological Entomology, 4, (1979) 239–47; Wilson, E. Caste and division of labor in leaf cutter ants—I. The overall pattern in A. Sexdens. Behavioral Ecology and Sociobiology 7, (1979) 143–56; Wilson, E., and Holldobler, B. The Ants. Belknap Press of Harvard University Press, Cambridge, MA 1990; Wilson, E., and Holldobler, B. Journey to the Ants. Belknap Press of Harvard University Press, Cambridge, MA 1994; Wirth, R., Herz, H., Ryel, R., Beyschlag, W., and Holldobler, B. Herbivory of Leaf-Cutting Ants. Springer, New York 2003. NAKED MOLE RAT Scientiﬁc name: Heterocephalus glaber Scientiﬁc classiﬁcation: Phylum: Chordata Class: Mammalia Order: Rodentia Family: Bathyergidae 14 EXTRAORDINARY ANIMALS Naked Mole Rat—A naked mole rat excavating soil at the face of one of the colony tunnels. (Mike Shanahan) What does it look like? Based on looks alone, the naked mole rat must surely rate as one of the most bizarre mammals. Except for a few sensory hairs and whiskers, it is completely bald, pink, and wrinkly. The head is large, but much of this bulk is taken up by the jaw muscles. Its eyes are minute and give it a squinting look. The lips of the animal close behind the huge, curved, ever-growing incisors. They have hairs between their toes, allowing them to use their feet like miniature brooms. Where does it live? This rodent is a burrow-dwelling creature of arid areas and savannah in parts of Kenya, Somalia, and Ethiopia. Where Females Rule The naked mole rat is a fascinating little mammal. These creatures shun the sky and do everything they need to underground in extensive burrow systems, which may have 4 km of tunnels. Some of these tunnels are just below the surface, while others can be more than 2 m underground. One of these tunnel networks is occupied by one colony of mole rats, which can contain between 70 and 300 individuals. Perhaps the most bizarre aspect of the naked mole rat’s life is the way that it reproduces. Like the bees, wasps, and ants, there is only one female in the mole rat colony that gives birth to young—the queen. No other mammal is known to reproduce in such a way. The queen may live for many years, producing as many as 900 pups in her lifetime, and it is very likely that all of these oﬀspring will stay with the colony as dispersal in these rodents is very rare indeed. With migration and immigration being so low, inbreeding in the nest is high, so most of the individuals in the colony will be very closely related to one another, which is also the case for bee, wasp, and ant colonies. As the queen has a monopoly on breeding, all of the other individuals in the colony help to rear the young, which are pro- duced proliﬁcally. The queen can produce a litter of pups every 80 days and can have ﬁve litters a year. The average number of pups in each litter is 12, but the record is 27, so you can see, these rodents know how to breed. Not only do the other colony members help to rear the young, but they are also responsible for ﬁnding food, tunnel making, maintaining the tunnels, and defending the colony. The other individuals in the colony have the biological apparatus needed for breeding, but their natural urges are somehow curbed. The animals all share a latrine where they defecate and urinate, and chemicals in the queen’s urine are responsible for suppressing the reproductive tendencies of the other females in the colony. STRENGTH IN NUMBERS 15 With their libido quashed by the queen’s urine, the other animals in the colony can concen- trate on more industrious tasks. Just after the rains, when the soil is softened, the naked mole rats begin some frantic team digging to enlarge and maintain the tunnel network. They form a chain gang, with a digger at the front putting its huge teeth and jaw muscles to good use to scrape away the tunnel face. Sweepers behind the digger brush the loose soil to their rear with their feet and shuﬄe backward, hugging the tunnel bottom until they reach the ejector mole rat that kicks the soil from the tunnel entrance, forming a molehill-like structure—the only clear, above ground evidence of these remarkable mammals. There are nine species of mole rat, all of which are found in sub-Saharan Africa. As their name implies, they are ratlike rodents that have become brilliantly adapted to an underground lifestyle. Although the mole rats have a very poor sense of sight, all of their other senses are very well developed. They have an exceptional sense of touch, feeling their way around their dark burrows with the long sensory hairs scattered all over their bodies. Not only does the naked mole have a peculiar social structure, but due to the stable temperature within its burrow systems, it is the only mammal that cannot regulate its own body temperature. It is eﬀectively cold-blooded. When naked mole rats are cold, they huddle together or bask for a while in the shallow tunnels. If they are too warm, they retreat to the deeper, cooler parts of the tunnel system. Temperature regulation is energetically expensive and requires a lot of food, but as the naked mole rat has abandoned this way of life, its appetite is small. It also grows more slowly than similarly sized mammals. Its metabolic rate is much lower than other small mammals, so its longevity is considerably extended. In captivity, queens can live for more than 20 years, which is astonishing for such a small mammal. Naked mole rats feed on roots and tubers located by burrowing through the soil. Some of these tubers are very large, and the mole rats make excavations into the nutritious interiors while leaving the skin intact, which allows the plant to survive and yield further food in the future. In some areas, the feeding activities of this animal can do a lot of damage to crops, especially sweet potatoes. Other mole rat species also chew through underground cables and undermine roadways when building their subterranean homes. To increase the nutrition that can be extracted from its food, the naked mole rat has a high density of bacteria in its gut, and to make digestion as eﬃcient as possible, it often eats its own feces. Feces are also fed to the young to inoculate their gut with the bacteria. The skin of naked mole rats lacks a chemical called substance P. All other mammals have this substance, which enables them to detect pain and injury to their skin. As a result, the mole rat feels no pain, in its skin at least. Why this should be is a mys- tery, but it may be because the mole rat lives in such tightly packed communities. In-ﬁghting in these communities would be very damaging to the colony as a whole; therefore, the lack of substance P could be a way of eliminating aggressive individu- als from the population. Since this rodent cannot detect wounds, molerats with a propensity for ﬁghting would get wounded, and as there is no sensation of pain, the injuries could easily be severe enough to cause the death of the animal from blood loss or infection. Another possibility for the lack of substance P is as a consequence of 16 EXTRAORDINARY ANIMALS the high levels of carbon dioxide in the mole rat tunnels due to all the frantic activity. Carbon dioxide at high concentrations can be painful to the lips, nostrils, and eyes; but as mole rats have no substance P, they feel nothing. Further Reading: Sherman, P. W., and Jarvis, J. U. The Biology of the Naked Mole-Rat. Princeton University Press, Princeton, NJ 1991. NEW ZEALAND BAT-FLY New Zealand Bat-Fly—The adult fly hitching a ride on the short-tailed bat. (Mike Shanahan) Scientiﬁc name: Mystacinobia zelandica Scientiﬁc classiﬁcation: Phylum: Arthropoda Class: Insecta Order: Diptera Family: Mystacinobiidae What does it look like? The bat-ﬂy is a wingless insect with rudimentary eyes and elaborate claws. The abdomen of the sexually mature females is swollen with ovaries and eggs. Where does it live? This ﬂy is found only on the northern tip of New Zealand’s North Island and only in association with the short-tailed bat, which lives in hollow trees. STRENGTH IN NUMBERS 17 A Fly that Does Not Fly Bats the world over are coveted by a variety of freeloaders. One group of animals in particular has been very successful in exploiting these small nocturnal mammals. Numerous ﬂy species, commonly known as bat-ﬂies, live on bats, typically sucking their blood with piercing mouthparts. However, on the island of New Zealand, there exists a bat-ﬂy that is very diﬀerent from the norm and that has struck up a remarkable relationship with the short-tailed bat, which is also native to New Zealand. Caves and other rocky nooks are in short supply on the northern tip of New Zealand’s North Island, so the short-tailed bat has taken to living in the hollows inside large trees, such as the giant, primitive kauris. In these woody refuges, the bats live together in small roosts. Alongside the bats lives the New Zealand bat-ﬂy, also in small colonies. The female ﬂies in the colony lay their eggs together in a nursery, and when the young maggots hatch they, too, stay close together. Unlike other bat-ﬂies, the New Zealand bat-ﬂy does not suck the blood of the bats it lives with, instead it gorges on the ﬂying mammal’s droppings. This excrement accumulates in the bottom of the roost and is known as guano. On this nutritious diet the ﬂies have time to engage in social activities. As the adult ﬂies and their young live side by side in the bat roost, the females will often sidle over to the crèche to groom their oﬀspring. The adults will also groom each other, cleaning and caressing their colony mates with their forelegs. Not only is this social and maternal behavior very peculiar, but there is also what appears to be the beginnings of a caste system, similar to the diﬀerent types of individual found in a colony of ants or termites. In the New Zealand bat-ﬂy colony, some of the males live beyond their normal reproductive age. These elderly males take on the role of colony guards, and if a hungry bat approaches the ﬂies too closely, the bat will be met with a cacophony of high-frequency buzzing produced by the guards. Occasionally, a colony of bat-ﬂies will become too big for the bat roost, so some will have to leave and found a new colony in another roost. To do this, they climb aboard one of the resting bats as it dangles from its perch and burrow into the bat’s fur. There they wait for the bat to begin its nighttime sorties in the hope that they will be ferried to another roost. As many as 10 bat-ﬂies can leave the nest in this way, clinging to the fur of one bat. The New Zealand bat-ﬂy is quite unlike the typical bat-ﬂies found in other parts of the world. The New Zealand bat-ﬂy is actually more closely related to the ﬂies known as blue bottles and green bottles. The species (Mystacinobia zelandica) was only discovered in 1973 by Beverly Hol- loway, a New Zealand entomologist, when a giant kauri tree in the Omahuta Kauri sanctuary fell over and an examination of its hollows revealed a roost of short-tailed bats and their ﬂy cohabitants. No other species of ﬂy shows this level of social behavior and maternal care. The ﬂies have been very successful at taking advantage of birds and mammals. Several types, known as keds, live on a range of mammal species, including domestic species like sheep. Many of these highly modiﬁed ﬂies move very quickly and with a sideways crablike gait. For people who work with sheep, the sheep ked is an unpleasant element of their job as its bite is particularly painful. Other species live on birds and have become very ﬂattened, which enables them to slip beneath the feathers of their avian hosts. Like ﬂeas, the parasitic ﬂies thrive on those animals that build nests, which pro- vides safety and food for their young. 18 EXTRAORDINARY ANIMALS The bat-ﬂy and the short-tailed bat are two examples of the unique fauna of New Zealand that has developed because of geological processes. Many millions of years ago, New Zea- land, Australia, Antarctica, and South America were fused into a huge landmass known as Gondwanaland. The animals and plants of this landmass evolved along a very diﬀerent path from those of the Northern Hemisphere. When Gondwanaland spit into the land- masses we see today, the ﬂora and fauna the landmasses carried evolved still further, but in isolation. Australia and South America have marsupials and an abundance of unique plant life. Antarctica was probably very similar, but its slow drift southward saw it fall into an icy grip. New Zealand, for some reason, had no land mammals apart from bats, and these may have colonized at a later date. In isolation, life ﬂourished, free from the tooth and claw of predatory mammals. Birds took to living on the ground. Insects evolved to ﬁll the niches occupied in other parts of the world by small mammals, and a host of primitive plants ﬂourished in the cool, moist climate. Sadly, this paradise was not to last forever, and the ar- rival of humans, ﬁrst Polynesians and then Europeans, spelled devastation and extinction. A second species of New Zealand bat-ﬂy lived in association with the greater short- tailed bat, but both became extinct when rats invaded Big South Cape Island in 1965. Further Reading: Holloway, B. A. A new bat-fly family from New Zealand (Diptera Mystacinobndae). New Zealand Journal of Zoology 3, (1976) 279–301. PORTUGUESE MAN-OF-WAR Portuguese Man-of-War—A stinging cell (nematocyst) shown closed (left) and discharged into the flesh of an animal (right). (Mike Shanahan) STRENGTH IN NUMBERS 19 Scientiﬁc name: Physalia physalis Scientiﬁc classiﬁcation: Phylum: Cnidaria Class: Hydrozoa Order: Siphonophora Family: Physaliidae What does it look like? The Portuguese man-of-war is very bizarre. It has a large gas-ﬁlled bladder, tinged with blue and pink, which can be 30 cm long. Dangling in the water, below this bladder, are many tentacles. Where does it live? This animal is found in many parts of the oceans and is frequently seen oﬀ the coast of Europe, North America, and Australia. It may prefer warm water, but ocean currents and storms will often push the man-of-war north and south. Life on the Ocean Waves The Portuguese man-of-war looks like some manner of jellyﬁsh. You could be forgiven for thinking this, and you wouldn’t be too far wrong. It is related to the jellyﬁsh, but it is a quite distinct collection of creatures. It is not a single animal, but a close-knit colony of four diﬀerent types of individual pol- yps, or zooids. The ﬁrst of these is the bladder polyp, which is responsible for producing the gaseous bladder that the colony uses as a buoyancy aid. The bladder is ﬁlled with mostly carbon monoxide, and in times of danger, it can be rapidly deﬂated so that the colony can sink out of reach of a po- tential predator. Not only does the bladder keep the Portuguese man-of-war aﬂoat but it also acts like the sail of a ship, catching the wind and carrying the colony around the seas. The second type of individual polyp in the colony is the feeder, whose job it is to catch food using tiny poison barbs, which can be shot into small ﬁsh and other sea animals. The feeders bear the long tentacles that hang below the Portuguese man-of-war, and when they catch some food, they contract, bringing the prey in reach of the tentacles of the third type of polyp—the gastrozooid, which is the stomach of colony that digests the food and provides nutrients for the rest of the polyps in the colony. The last type of polyp is the gonozooid, whose job it is to make more colonies, producing small larvae that grow to become the buoyancy bladder and the other three zooids of a complete colony. The way in which the Portuguese man-of-war catches its prey is very interesting. The ﬁshing tentacles of the colony, the dactylozooids, are armed with thousands upon thousands of stinging structures called nematocysts. These are beautifully adapted hunting tools. The stinger, produced by a special type of cell, looks like a small bulb, and inside it is a coiled thread. On the outside of the stinger, in the water, is a tiny hair trigger. An animal will brush past this hair and cause the bulb to ﬁre, which it is does with astonishing ferocity. The coiled thread is shot from the bulb at a velocity of 2 m per second, and for something so small, this means its tip is accelerating at 40,000 Gs (by com- parison, a race-car driver experiences 2–3 Gs speeding around a corner). The thread penetrates the prey and injects potent venom. A larger animal could tolerate the eﬀect of one of these cells, but there is strength in numbers, and hundreds or thousands of nematocysts are ﬁred at once. The venom is neurotoxic, and it rapidly paralyzes the prey so that it can be easily transferred to the gastrozooids. The phylum Cnidaria is a fascinating group of animals numbering more than 10,000 species. The Portuguese man-of-war is but one of these, and its relatives, such as the typical jellyﬁsh and the anemones, are very familiar animals whose beauty can only be appreciated when they are seen in water. Their soft bodies, composed mostly of water, 20 EXTRAORDINARY ANIMALS lose their shape when they are washed up on the shore, rendering them little Go Look! more than featureless blobs. If you live near the coast in the eastern United States, The cnidarians are an ancient group you may be lucky enough to see a Portuguese man-of- with the longest fossil history of any war colony washed up on the shore or still ﬂoating in a animal, extending back over 700 million pool left by the retreating tide. Because of their bladders, they are at the mercy of the wind and the ocean currents, years. Although anatomically simple and several may be found on a single beach after a storm. animals, they successfully compete with You will notice the bladder with its pink/blue tinge and organisms much more complex than the tentacles hanging from its underside. The longer ones themselves. are the ﬁshing tentacles. Be careful not to touch the ten- The venom of cnidarians is very toxic. tacles, because even if the animal is dead or washed up That of the Portuguese man-of-war on the shore, the stinging cells are still active and will be discharged at the slightest touch. can cause some very painful injuries if a swimmer accidentally brushes against the long ﬁshing tentacles. The pain is extreme and immediate, and the sting can even be fatal to the young, elderly, and people with certain allergies. The victim should be taken from the water, and an ice-pack should be placed on the aﬀected area, but in no circumstances must the sting be washed with vinegar (a common treatment for some other jellyﬁsh stings). Although the sting of the Portuguese man-of-war should be treated with respect, it is by no means the most dangerous of the venomous cnidarians. This title belongs to the sea wasp, also known as the box jellyﬁsh, which is frequently found in the waters oﬀ Australia and forces swimmers from the water. This animal has caused at least 64 deaths since 1884. Death, if it occurs, happens 3–20 minutes after stinging. The wounds caused by nonlethal stings can be severe and often take a long time to heal. The reason that these innocuous-looking blobs of jelly have such lethal toxins is that they do not have limbs, or anything for that matter, with which to grab and immobi- lize prey; therefore, they use fast-acting, paralyzing venom. The Portuguese man-of-war has developed an interesting relationship with several types of ﬁsh, including the shepherd ﬁsh, the clown ﬁsh, and the yellow jack, species which are rarely found elsewhere. The ﬁsh accompany the colony on its travels around the high seas. The clown ﬁsh can swim among the tentacles with impunity, very likely made possible thanks to skin mucus, which does not stimulate the hair triggers of the stingers. The shepherd ﬁsh seems to avoid the larger ﬁshing tentacles and will feed on the smaller tentacles directly beneath the bladder. The presence of these ﬁsh may at- tract other animals on which the Portuguese man-of-war can feed. The name Portuguese man-of-war comes from the likeness of the gas bladder of the colony to the sail of the old Portuguese ﬁghting ships. SPONGES Scientiﬁc name: Porifera Scientiﬁc classiﬁcation: Phylum: Porifera Class: Calcispongiae, Hyalospongiae, Demospongiae, Sclerospongiae STRENGTH IN NUMBERS 21 Sponges—A section through a sponge chamber showing the various types of cell, including the Sponges—A stovepipe sponge photographed in the collar cells (inset). (Mike Shanahan) Caribbean. (Bart Hazes) What do they look like? The sponges have a ﬁbrous body wall, which can be a variety of bright colors. They can be encrusting or upright and branching, and a whole host of shapes in between. Their very odd body plan is built around an elaborate network of water canals. Where do they live? Sponges are aquatic animals and can be found in both marine and freshwa- ter habitats, although the vast majority are found in the former. They are normally found in shallow water the world over, although some species can be found in the cold, dark depths. Successful Simplicity In aquatic habitats throughout the world, sponges abound. To the uninitiated, sponges look like plants or small geological features. Some cling to rocks, while others extend out into the water, forming thin turrets or broad columns. Nothing in the outward appearance of these peculiar organisms gives any indication that they are in fact animals. Among the animals, the sponges are the most primitive group, and to see what makes them an animal, one look must look at them very closely. There are no organs within a sponge, just a network of cavities and canals. Lining the sponge’s cavities there are so-called collar cells, which drive a current of water through the animal’s body and latch onto and ﬁlter whatever edible particles may be suspended in the water. The water-pumping ability of even a small sponge is very impressive. Each day, a 10 cm long spec- imen is capable of channeling more than 22L of water through the network of collar-cell-lined chambers, which may number more than 2 million. Most of the particles ingested by the sponge are very tiny, even too small for a conventional microscope to see. These particles are absorbed by another type of cell that looks a lot like an amoeba. As well as playing a role in digestion, these cells also have the ability to turn into any one of the other cells that make a fully functioning sponge. The outside of these animals is pocked with numerous pores and holes linking the interior of the animal to the surrounding water. Other cells in the sponge secrete an elaborate, glassy skel- eton of silica, while others secrete a protein called spongin that ﬂeshes out the frame. In many ways, the sponge is simply an assemblage of diﬀerent types of cells, and although there is a division of labor among these units, similar to that seen in other animals, the diﬀerentiation is nowhere near as complex. The simplicity of the sponge makes it a champion of regeneration. The 22 EXTRAORDINARY ANIMALS tissue of a living sponge can be forced through a silk mesh, turning the animal into a so-called cell soup. Other animals would be very hard pressed to recover from such brutal treatment, but the sponge’s separated cells quickly reorganize, forming themselves into several new sponges. In commercial sponge-growing enterprises, a large specimen may be cut into pieces, which are at- tached to cement blocks and then submerged. Each piece grows into a new sponge, which can be harvested after a few years. These bizarre and simple creatures were probably among life’s ﬁrst attempts at an organ- ism with numerous cells instead of just one, but they developed along a track that spawned no descendents. They are, in an evolutionary sense, a dead end. There are more than 5,000 species of sponge, and only around 150 of these can be found in freshwater. The rest are marine animals and can be found wherever there are suitable surfaces for them to attach to. They range in size from tiny species only a few millimeters long with an internal scaﬀold of calcium carbonate, to huge loggerhead sponges, which may be more than a meter long and wide. It was only in the midseventeenth century that naturalists ﬁrst saw the circulation of water inside sponges, an observation that singled them out as animals. Up until this time, the lack of any obvious movement and their odd internal structure led natural- ists to label sponges as plants. The earliest sponge fossils are at least 500 million years old, and there are claims of even older fossils. Regardless of when they appeared, sponges were at the peak of their success during the Cretaceous period. Along with their high silica content and the spiky nature of their skeletons, many spe- cies of sponges contain noxious substances to further deter potential predators. Even with this armory of defenses, many animals eat sponges, and some have specialized on a diet consisting solely of sponges. The sea turtles are a good example. The feces of certain turtles may contain more than 95 percent sponge fragments. A sponge larva is a free-swimming animal, albeit brieﬂy. It swims out of its parent and ﬂoats in the water for a short time before settling and developing into the familiar creature. The complex internal arrangement of the sponges makes the larger species excellent refuges for a number of delicate aquatic animals. One large loggerhead sponge was found to contain more than 16,000 shrimps. In a very interesting relationship some species of freshwater sponge are preyed upon by small insects known as sponge ﬂies, which are, in fact, close relatives of lacewings. The female sponge ﬂy lays her eggs on vegetation overhanging water. The larvae drop into the water and seek out a sponge to feed on. The larvae of some species cling to the surface of the sponge, while others explore the sheltered conﬁnes of the sponge’s internal cavities. Sponges have long been of commercial value to people all around the world. The larger, cylindrical forms are valued as bathroom accessories or trinkets, although decreasingly so in the former use due to the availability of synthetic sponge. The interesting biochemistry of sponges has also attracted interest, and many compounds extracted from these animals are being investigated as starting points for novel medicines. STRENGTH IN NUMBERS 23 STONY CORALS Stony Corals—A close up view of a tiny coral Stony Corals—A number of stony coral species can polyp showing the tentacles that identify it as a be seen here, showing the diversity of this type of relative of jellyfish. (Mike Shanahan) colonial animal. (Bart Hazes) Scientiﬁc name: Scleractinia Scientiﬁc classiﬁcation: Phylum: Cnidaria Class: Anthozoa Order: Scleratinia Family: several What do they look like? Corals grow in a huge variety of forms. They can be thin and branch- ing, moundlike, ﬂat and spreading like a tabletop, and every intermediate form in between. They can be small and self-contained or huge rambling structures. The animal responsible for these structures, the coral polyp, is a tiny anemone-like creature, with a short, squat body crowned with numerous tentacles. Where do they live? The stony corals are found throughout the world’s oceans but are at their most impressive in the warm, shallow waters of the tropics and subtropics. The Indo-Paciﬁc region, including the Red Sea, Indian Ocean, Southeast Asia, and the Paciﬁc, accounts for the greatest abundance of stony corals. Many Polyps Build Great Structures The animal responsible for producing coral is one of the most inconspicuous creatures; yet its activities can fashion whole ecosystems and change the earth’s climate. To the uninitiated, a stony coral looks like a rock, a dead, inanimate object; however, on closer inspection, the outer surface is actually a thin, living veneer. Pitting its surface are numerous small pores or cups, each containing a small polyp, 1–3 mm across. This polyp looks like a small sea anemone, nes- tled in a receptacle of calcium carbonate of it own creation. Only the animal’s feeding tentacles project from this cup, and even these can be withdrawn and tucked out of the way of hungry sea animals. The polyps, like all jellyﬁsh and their kin, are predatory. The tentacles of many 24 EXTRAORDINARY ANIMALS species wave serenely in the current, waiting for prey ranging from microscopic ﬂoating animals to small ﬁsh to come within range of their batteries of explosive stinging cells. Other species secrete copious quantities of mucus to entrap tiny prey and edible particles. The prey, paralyzed by the powerful venom, is transferred to the polyp’s equivalent of a mouth. Another source of nourishment comes from an interesting relationship many polyps have struck up with various forms of single-celled, algaelike organisms. These algal cells live within the cells lining the pol- yp’s digestive cavity, and via the process of photosynthesis, they produce sugars and other nutri- ents, a proportion of which goes to the polyp. With a nourishing diet, the polyps grow quickly, constantly adding more calcium carbonate to their little cups. It is these small limestone cups that are the building blocks of a coral colony. Over decades, centuries, and even millennia, suc- cessive generations of polyps lay down layer after layer of calcium carbonate until the thin living layer surrounds a huge skeleton of what is essentially rock. The rate of colony growth achieved by the minute polyps, considering they are secreting rock, is extraordinary. Some of the branch- ing corals can grow in height or length by as much as 10 cm per year (about the same rate at which human hair grows). Other corals, like the dome and plate species, are more bulky and may only grow by 0.3 to 2 cm per year. This may not seem like much, but it can be sustained for thousands of years, forming huge and complex reefs. The Great Barrier Reef, oﬀ the coast of Australia, is the largest reef complex in the world and is composed of a multitude of coral colo- nies. The structure we see today is thought to be 6,000–8,000 years old, although the modern structure has developed on a much older reef system, thought to be 500 million years old. This huge reef system stretches for over 2,000 km and can be seen from space. Reefs like the Great Barrier Reef support huge numbers of marine organisms, and by aﬀecting the direction and ﬂow of currents, they directly aﬀect the earth’s climate—all of this from the tireless deposition of rock by a minute sea creature. The stony corals are divided into reef-building species and solitary species. The for- mer are the more familiar as they are found in shallow water and support huge assem- blages of marine organisms. The latter are found throughout the world’s oceans, even down to depths as great as 6,000 m. In a coral colony, all of the polyps are genetically identical. They are all connected by a network of channels allowing the sharing of nutrients and symbiotic algae. For much of the year, corals reproduce asexually. Either they spilt down the middle, producing two identical individuals each regenerating the missing half, or the crown of tentacles around the top of a polyp develops a small bud, which grows into a min- iature polyp that is eventually released. At other times of the year, dictated by the phases of the moon, huge numbers of eggs and sperm are released by female and male polyps or hermaphrodite polyps with both sets of sex organs. The eggs are fertilized, and the resulting larvae drift through the water in the hope of eventually founding another colony in a suitable location. The ecosystems formed by stony coral reefs are some of the most diverse habitats on the planet. They are rich in nutrients and provide an intricate maze of hidey-holes for marine animals. For example, the Great Barrier Reef is composed of at least 400 spe-

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