Forensic Entomology Forensic Entomology

1 Forensic Entomology

Objectives

You will understand: The stages of death. The role insects play in the decomposition of carrion. Postmortem interval and how it is estimated. The life cycle of insects. How variables affect results of scientific experiments.

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Objectives, continued You will be able to: Distinguish among major insect types associated with carrion. Identify the relationship between insect type and the stages of death. Estimate time of death.

3 Forensic Entomology

Taxonomy Classification of Things in an Orderly Way

We are interested in the phylum, Arthropoda; class, Insecta; order:

Diptera (flies) Coleoptera (beetles) 4 Forensic Entomology

Forensic Entomology

Entomology is the study of insects. Forensic entomology involves the use of insects and other arthropods to aid in legal investigations. There are three areas of application: Insect damage to structures Infestation of foodstuffs Insects that inhabit human remains

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The Process of Death Algor Mortis: Body cooling rate

Hours since death = 98.4°F – internal body temperature 1.5 Livor Mortis: skin discoloration caused by pooling of blood Rigor Mortis: rigidity of skeletal muscles

Temperature of body Stiffness of body Time since death Warm Not stiff Not dead more than 3 hours

Warm Stiff Dead between 3 and 8 hours

Cold Stiff Dead between 8 and 36 hours Cold Not stiff Dead for more than 36 hours

A pathologist estimates time of death from these factors.

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ALGOR MORTIS • The most accurate means for taking body temp is internally (rectal). • At a scene, they use the liver. • This reading is accomplished by inserting a meat thermometer into the body just under the rib cage on the right side. • In most cases, a person has been dead for so long that the body temperature may be so low as to be irrelevant. • The preferred time window for evaluating algor mortis is within the first several hours after death. • Beyond that, the rate of cooling becomes less and less accurate as the body temperature approaches equilibrium • Body temperature is easily affected by: • Age • Weight • Illness • Conditions of the environment (temperature, clothing, surface, activity prior to death)

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ALGOR MORTIS PROBLEMS Temperatures can also increase due to physiology or environment. • Someone who dies with a high fever has a higher plateau from which to cool and will subsequently give a higher reading. • Someone who dies in a heated bedroom will cool more slowly than someone in an unheated garage.

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RIGOR MORTIS • Stiffening is called rigor mortis. • Depending on temperature and other conditions, rigor mortis lasts approximately 72 hours.

9 Forensic Entomology RIGOR MORTIS: How it Works • Normal living muscle cells use energy (in the form of ATP) to move Ca out of the cells. • At death, your ATP reserves are used up quickly and Ca can’t get shipped out the cell…it builds up inside. • The Ca build-up causes ACTIN and MYOSIN (muscle fibers) to link and stay linked. 10 Forensic Entomology

RIGOR MORTIS: TIMELINE • Range from 10 min to several hrs.

• Maximum stiffness is reached around 12- 24 hours post mortem.

• Facial muscles are affected first, with the rigor then spreading to other parts of the body.

• It is interesting to note that meat is generally considered to be more tender if it is eaten after rigor mortis has passed.

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LIVOR MORTIS Discoloration - Livor • Red blood cells – Mortis • Lividity appears in hues of red • Cherry red = CO poisoning • Maroon is normal • If lividity appears on the front but the corpse is on its back = the corpse was moved PM. • The lividity will “pattern”, based on if the body is lying on an object.

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The Process of Death, continued

Stage Description The cadaver appears fresh externally but is Initial or fresh decay (autolysis) decomposing internally due to the activities of bacteria present before death (0–4 days). The cadaver is swollen by gas produced internally, Putrefaction or bloating accompanied by the odor of decaying flesh (4–10 days). Flesh of creamy consistency, with exposed body parts black. Body collapses as gases escape. Black putrefaction Fluids drain from body. Odor of decay very strong (10–20 days). Cadaver drying out. Some flesh remains Butyric fermentation at first; cheesy odor from butyric acid (20–50 days). Cadaver almost dry; slow rate of decay. May Dry decay (diagenesis) mummify (50–365 days).

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Life Cycle of Insects Metamorphosis egg

larva (maggot)

The life cycle of Musca domestica pupa

winged adult

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Time of Death Insects arrive at a decomposing body in a particular order (succession) and then complete their life cycle based on the surrounding temperature. By collecting and studying the types of insects found on a body and their metamorphic stage, a forensic entomologist can estimate the time of death.

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Variables Affecting Metamorphosis Temperature The higher the temperature (within limits), the faster the growth.

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Variables Affecting Metamorphosis, continued Habitat Fly species can vary geographically according to climate, season, and habitat.

Phormia regina Lucilia illustris

For example, the fly pictured on the left prefers shade; the one on the right, sunlit areas.

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Collection of Evidence

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