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Forensic Entomology

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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.

Objectives

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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.

Objectives, continued

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TaxonomyClassification of Things in an Orderly Way

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

Diptera (flies) Coleoptera (beetles)

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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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98.4°F – internal body temperature

1.5Hours since death =

The Process of Death

Algor Mortis: Body cooling rate

Livor Mortis: skin discoloration caused by pooling of blood

Rigor Mortis: rigidity of skeletal muscles

A pathologist estimates time of death from these factors.

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

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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 PROBLEMSTemperatures 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.

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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.

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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 MORTISDiscoloration - 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

Initial or fresh decay (autolysis)

The cadaver appears fresh externally but is

decomposing internally due to the activities of bacteria present before death (0–4 days).

Putrefaction or bloating

The cadaver is swollen by gas produced internally,

accompanied by the odor of decaying flesh (4–10 days).

Black putrefaction

Flesh of creamy consistency, with exposed body

parts black. Body collapses as gases escape. Fluids drain from body. Odor of decay very strong (10–20 days).

Butyric fermentation

Cadaver drying out. Some flesh remains

at first; cheesy odor from butyric acid (20–50 days).

Dry decay (diagenesis)Cadaver almost dry; slow rate of decay. May

mummify (50–365 days).

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Life Cycle of Insects

Metamorphosis

egg

larva (maggot)

pupa

winged adult

The life cycle of

Musca domestica

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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.

Time of Death

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Variables Affecting Metamorphosis

TemperatureThe higher the temperature (within limits), the faster the growth.

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Variables Affecting Metamorphosis, continued

HabitatFly species can vary geographically according to climate,

season, and habitat.

For example, the fly pictured on the left prefers shade; the one on

the right, sunlit areas.

Phormia regina Lucilia illustris

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Collection of Evidence