Forensic Entomology

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Forensic Entomology

• NAHS Biology
• Lorin Somerlot, 2007

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What is a Forensic Entomologist?

• A scientists who uses insects to help solve
  crime.

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How do insects help solve crimes?

• A dead body attracts insects
• Insects lay eggs on the body.
• Hatching larva use body as food.
• Larva grow at a predictable rate.
• The Postmortum Interval (PMI-how long the body
  has been dead) can be determined by measuring and
  identifying the developing larva.

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Insect Succession

• Can be used to determine PMI
• Different species of insects prefer different
  stages of decomposition

I prefer my corpse dried
The fresher the better!
Juicy and smelly suits me just fine!
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Stages of Decomposition

• Living
• Initial decay
• Putrefaction
• Black putrefaction
• Butyric fermentation
• Dry decay

• http//www.deathonline.net/decomposition/movies/qu
  icktime/timelapse.mov - time-lapse of
  decomposition

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Initial Decay--Day 1-3

• Bacteria, present in the intestine to digest
  food, begin to eat away at the intestine itself.
• Intestine decays releasing bacteria and digestive
  enzymes into body cavity.
• Blow flies and house flies immediately begin to
  lay eggs on the defenseless body.

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Putrefaction--Day 4-8

• Bacteria continue to break down body producing
  large amounts of gasses.
• Gasses inflate the body like a balloon.
• Larval flies move throughout the body, eating the
  partially digested flesh.
• Smell attracts other species flies and beetles.
• Rate of decay increases.

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Black Putrefaction 10-20 days after death

• Bloated body collapses and flattens.
• Large amounts of fluids are released.
• Flesh is creamy and black where exposed.
• Several generations of flies are present.
• Wasps parasitize maggots.

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Butyric Fermentation 20-50 days after death

• Remaining flesh is decomposed and corpse begins
  to dry out.
• Cheesy smell attracts new organisms.
• Body ferments and is covered with mold.
• Hardening of body makes it difficult for maggots
  to feed.
• Chewing beetles and their larva move in.

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Dry Decay 50-365 days after death

• Body is dry and decays slowly.
• Hair and bones are all that remain.
• Hair is fed on my moths and bacteria.
• Mites may be present and feed on bacteria.

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Insect Succession
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Factors that affect decay rate and growth rate of
flies

• Temperature--the warmer the climate, the faster
  the decay.
• Season--early spring will decay slower, because
  the insect population is still relatively low.
• Degree of corpse enclosure--the more exposed, the
  faster the decay.

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Classification of a House Fly

• Kingdom - Animal
• Phylum - Arthropods
• Class - Insects
• Order - Diptera (All Flies)
• Family - Muscidae
• Genus - Musca
• Species - domestica

Musca domestica
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Life Cycle of a Fly

• Flies lay 100-150 eggs at a time.
• Eggs hatch-1st instar
• Larva molt-2nd instar
• Larva molt again-3rd instar
• Pupa -- cocoon
• Adult fly

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Another Look
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One more time!
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Egg Stage

• Most flies lay 100-150 eggs at a time.
• The eggs are small and oblong.
• They are white or cream colored.
• It takes 8-14 hours for the eggs to hatch after
  they have been laid.
• Flies only lay eggs in daylight.

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Another look at eggs
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Larva

• Molt (shed their skin) twice after hatching.
• Breath through anterior and posterior slits
  called spiracles

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Instar Maturation of Larva

• 1st instar larva take 8-14 more hours until they
  are ready to molt.
• 2nd instar larva take 2-3 days to molt.
• 3rd instar larva take 7-8 days until pupal
  maturation.

Pre-pupal 3rd instar larva.
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Spiracles are distinct

• Different species of fly larva have different
  spiracle characteristics

Peritreme
Spiracular Slits
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Pupa

• Once larva mature they stop eating and
  metamorphose into an adult fly.

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Basic Anatomy of an Adult Fly

• Insects have three body parts
• Head
• Thorax
• Abdomen
• Six Legs
• Wings

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Identifying Adult Flies
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Identifying Adult Flies
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Identifying Adult Flies
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Identifying Adult Flies
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Identifying Maggots by Spiracular Slits

• Maggots can be identified by their distinguishing
  spiracular slits.

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Spiracular Slits