Forensic Entomology

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Forensic Entomology

• Maggots and Time of Death Estimation

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(No Transcript)
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Entomology is the Study of Insects Images from
www.afpmb.org/military_entomology/usarmyento/files
/ArmyEntomology.ppt
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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.

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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

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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.

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Forensic Entomology is Applied Biology

• If it werent 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

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Image http//www.nlm.nih.gov/visibleproofs
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Time of Death can be broadly estimated up to
about 36 hours
Temperature Stiffness Time of death
Warm Not stiff Not dead
more
than three hours
Warm Stiff Dead between 3

to 8 hours
Cold Stiff Dead between 8

to 36 hours
Cold Not stiff Dead in more

than 36 hours
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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

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Image http//www.nlm.nih.gov/visibleproofs
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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 16101890 1540
3rd Instar Pupa 70 F 130 130 x 70 9100 ADH 16101890 15409100
Pupa Adult Fly 70 F 143 143 x 70 10010 ADH 16101890 15409100 10010
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Five Stages of Decomposition Fueled by Insect
Activity.

• Fresh
• Bloat
• Decay
• Post-decay
• Dry (skeletal)

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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)

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Bloat

• Swells due to gases produced by bacteria
• Temperature rise of the corpse
• Flies still present house flies join
• (Muscidae)

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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 its original mass.

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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.

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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.

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Arrival

• First flies search our natural orifices
• Mouth, nostrils, eyes, ears, genitals
• Trunk of body is invaded later
• This can determine foul play

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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)