Forensic Science 1 - Entomology Notes PDF

Name: _____________________ Date: ________________ Forensic Science 1 Mrs. Paulik UNIT 6 - NOTES - Entomology Learning Objectives: Explain how insect evidence can help establish postmortem interval (PMI...

Name: _____________________ Date: ________________ Forensic Science 1 Mrs. Paulik UNIT 6 - NOTES - Entomology Learning Objectives: Explain how insect evidence can help establish postmortem interval (PMI) Explain how the forensic entomologist interprets insect evidence and applies environmental variables to answer questions about a dead body and the crime. 1  Entomology = the study of insects and their relationship to crime scenes ○ used to estimate time of death & PMI ○ collects insect evidence on, above, below victim’s body as well as insect evidence from the immediate area around the victim ○ collects data about environmental conditions around the body as well as below it ex: temperature, moisture, wind 2 Insect Life Cycle Complete Metamorphosis (ex: blowfly): ○ egg → maggot/larva(e) → pupa(e) → adult Incomplete Metamorphosis (ex: grasshopper, dragonfly, cockroach): ○ egg→ nymph → adult Changes involve shedding the exoskeleton (the external skeleton that protects & supports the insect) affected by fluctuations in daily environmental conditions within minutes of death, insects lay eggs on warm body in orifices or wounds because they are attracted by the smell of first stages of 3 decomposition  4 types of insects found on dead remains: ○ Necrophagous = feed directly on the remains ○ Predators and Parasites = feed on the necrophagous species but not the remains ○ Omnivorous = feed both on the remains and the resident species ○ Adventive = use the remains as part of their habitat 4  Blowflies = are one of the first insects to arrive a dead body ○ Entomologists can determine PMI because they know how long it takes for the various stages of development at given temperatures ○ Ex: if corpse contains blowfly eggs (and no larvae, pupae or adults), then the approximate time of death would be 24 hours or less ○ Ex: if corpse contains pupae (and no adults), then the approximate time of death would be 130 to 143 hours. 5  Accumulated Degree Hours (ADH) = the amount of total heat accumulated by a larvae to complete developmental stages, varies by species ○ Ex: the Green Bottle Blowfly (Phaenicia sericata) needs about 200 total ADH to complete its development while the Bluebottle Blowfly (Calliphora vomitoria) requires over 700 ADH to reach the same stage of development 6 1) Using the plot for the green bottle fly (Lucilia sericata), the largest larva removed from body was found to be 4.1 mm. If the body were found indoors by a partially open window and the temperature was constant was at 70° F, what would be the age of this larva (Note: the grid lines on the plot are for degrees C while the temp in F is shown at right side in the plot)? Answer: 1 day 7 2) Using the plot at right for the green bottle fly (Lucilia sericata), the largest larva removed from body was found to be 8 mm. If the body were found indoors by a partially open window and the temperature was constant was at 70° F, what would be the age of this larva (Note: the grid lines on the plot are for degrees C and the temp in F is shown at right in the plot)? Answer: 2 days 8  Insects are collected at crime scenes, placed in specimen jars and are often raised in laboratory under same environmental conditions as those found at the crime scene to provide a more accurate estimate of time of death If insects from another geographical region are found on the body, it suggests the corpse may have been moved. 9 Limitations of Forensic Entomology Time of death estimates depend on accurate temperature information, but local weather patterns can be variable. In winter, there are fewer insects so less available evidence Since it takes time to rear insects, you can’t produce immediate results. Treatments (like freezing, burial or wrapping) that exclude insects can affect estimates. Since chemicals can slow or accelerate growth, insect evidence may be affected by the presence of drugs in a corpse's system. 10 Factors Influencing Rate of Decomposition Studied at The University of Tennessee – Knoxville – Forensic Anthropological Research Facility (“The Body Farm”) age- young individuals decompose faster than elderly individuals illness- sick individuals decompose faster than healthy individuals weight- overweight individuals decompose faster than normal weight individuals clothing– unclothed individuals decompose faster than clothed individuals temperature– cold environments slow bacterial growth & decomposition 11 Stages of Decomposition Step 1 of 5: Fresh / Initial ○ ~T.O.D. – several days postmortem ○ Corpse appears normal on the outside but is starting to breakdown from the actions of bacteria and autolysis. ○ Pallor mortis, algor mortis, livor mortis, rigor mortis & corneal clouding take place ○ Insects start to arrive at body and lay eggs 12 Stages of Decomposition Step 2 of 5: Bloating / Putrefaction ○ ~2-6 days postmortem ○ pronounced discoloration due to livor mortis ○ The skin becomes marbled in coloration ○ large amount of gas produced from anaerobic bacterial action inflates the body cavities, especially the intestines and abdomen ○ body cavity may split open from collected gases, resulting in fluid seepage. ○ Odor of decaying flesh is present and the corpse appears swollen. ○ Insect activity increases 13 Stages of Decomposition Step 3 of 5: Active Decay / Black Putrefaction ○ ~7+ days postmortem ○ very strong rotting odor ○ flesh is discolored ○ skin is rupturing, allowing gases to escape and body to collapse while seepage of fluid continues ○ most body mass is lost to insect activity; maggots feed internally and externally ○ tissues deplete leaving only skin, cartilage, bone, hair and teeth 14 Stages of Decomposition Step 4 of 5: Post-Decay / Advanced Decay ○ several weeks to months postmortem ○ corpse is drying out and most flesh is gone. ○ fewer insects remain (the larvae have consumed most of the soft tissues and flesh and have reached the developmental stage where they leave the body to pupate) 15 Stages of Decomposition Step 5 of 5: Dry or Skeletal ○ months to years postmortem ○ Insects that have evolved mechanisms for digesting keratin (a tough, insoluble protein found in hair, fingernails, and other resistant tissues) are the primary inhabitants of the body ○ At the end of the process, very little besides bones and teeth remains 16