Post on 17-Jun-2020
Forensic Entomology
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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