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Forensic Entomology
Maggots and Time of Death Estimation
Entomology is the Study of Insects
Images from: www.afpmb.org/military_entomology/usarmyento/files/ArmyEntomology.ppt
Insect Biology
• Insects are the most diverse and abundant forms of life on earth.
• There are over a million described species- more than 2/3 of all known organisms
• There is more total biomass of insects than of humans.
Medicolegal Forensic Entomology
• Often focuses on violent crimes– Determination of the time (postmortem
interval or PMI) or site of human death based on identification of arthropods collected from or near corpses.
– Cases involving possible sudden death– Traffic accidents with no immediately
obvious cause– Possible criminal misuse of insects
Postmortem interval (PMI)
• Forensic Entomology is used to determine time since death (the time between death and corpse discovery)
• This is called postmortem interval or PMI).
• Other uses include• movement of the corpse• manner and cause of death• association of suspects with the death scene• detection of toxins, drugs, or even the DNA
of the victim through analysis of insect larvae.
Forensic Entomology is Applied Biology
• If it weren’t for decomposition of all living things, our world would fill up with dead bodies.
• When an animal dies, female insects will be attracted to the body. They enter exposed orifices or wounds and lay eggs or larvae.
• A forensic entomologist:– identifies the immature insects– determines the size and development of the
insects– calculates the growth of the insects and passage
through stages of the life cycle in laboratory– compares the growth against weather conditions
to estimate time of oviposition
Image: http://www.nlm.nih.gov/visibleproofs
Time of Death can be broadly estimated up to about 36
hoursTemperature Stiffness Time of deathTemperature Stiffness Time of deathWarm Not stiff Not dead more than three hoursWarm Not stiff Not dead more than three hours
Warm Stiff Dead between 3 to 8 hours Warm Stiff Dead between 3 to 8 hours
Cold Stiff Dead between 8 to 36 hoursCold Stiff Dead between 8 to 36 hours
Cold Not stiff Dead in more than 36 hoursCold Not stiff Dead in more than 36 hours
Differentiate between PMI and Time of Death
• These may not always equate. • Post mortem interval is restricted to
the time that the corpse or body has been exposed to an environment which would allow insect activity to begin. – Closed windows– Body in box or bag– Cold temperatures– Deeper burial
Image: http://www.nlm.nih.gov/visibleproofs
Calculating PMI from Accumulated Degree Hours
(ADH)From To Temp
Hours
ADH Cumulative ADH
Egg 1st Instar 70° F 23 23 x 70=1610 ADH
1610
1st Instar 2nd Instar
70 ° F 27 27 x 70=1890 ADH
1610+1890
2nd Instar
3rd Instar
70 ° F 22 22 x 70=1540 ADH
1610+1890+1540
3rd Instar
Pupa 70 ° F 130 130 x 70=
9100 ADH
1610+1890+1540+9100
Pupa Adult Fly 70 ° F 143 143 x 70=
10010 ADH
1610+1890+1540+9100+10010
Five Stages of Decomposition Fueled by Insect Activity.
• Fresh• Bloat• Decay• Post-decay• Dry (skeletal)
Fresh
• Begins at death• Flies begin to
arrive within 10 mins
• Temperature falls to that of the ambient temperature.
• Blow flies– (Calliphoridae)
• Flesh flies – (Sarcophagidae)
Bloat
• Swells due to gases produced by bacteria
• Temperature rise of the corpse
• Flies still present – house flies join– (Muscidae)
Decay• Gases subside,
decomposition fluids seep from body.
• Bacteria and maggots break through the skin.
• Large maggot masses and extreme amounts of fluid.
• Unpleasant odor• Larvae beginning to
pupate.• Corpse reduced to
about 20% of it’s original mass.
Post-Decay
• Carcass reduced to hair, skin, and bones.
• Fly population reduced and replaced by other arthropods.
• Hide beetles are dominant in dry environments.
• Mite and predatory beetle populations increase.
Dry (Skeletal)
• Does not always occur especially if corpse is in a wet region. Maggots will stay longer and hide beetles will not appear.
• In wet environments the hide beetles are replaced with nabid and reduviid insects.
• The corpse is reduced to at least ten percent of the original mass.
• In the last stage (Skeletal Stage), only bone and hair remain.
Arrival
• First flies search our natural orifices– Mouth, nostrils, eyes, ears, genitals
• Trunk of body is invaded later• This can determine foul play
Factors that Affect Rate
• The following things can affect the rate of growth:– Drugs present in the body– Temperature– Location of the body (urban/rural
determines species)