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Forensic Entomology
STEM
What is a Forensic
Entomologist?
• A scientists who uses insects to help
solve crime.
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 Post-Mortem Interval (PMI-how long
the body has been dead) can be
determined by measuring and identifying
the developing larva.
Forensic Entomology - The Crime Scene Video
Insect Succession
• Can be used to determine PMI
• Different species of insects prefer
different stages of decomposition
“The fresher
the better!”
“Juicy and smelly
suits me just fine!”
“I prefer my
corpse dried”
Stages of Decomposition
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Living
Initial decay
Putrefaction
Black putrefaction
Butyric fermentation
Dry decay
• http://australianm
useum.net.au/m
ovie/Stages-ofdecomposition/
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.
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.
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.
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.
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.
Insect Succession
Body Condition
Species Present
Fresh
Blow Fly
House Fly
Screw Worm Fly
Hairy Maggot Fly
Flesh Fly
Bottle Fly
Bloated
Blow Fly
Flesh Fly
Hairy Maggot Fly
House Fly
Bottle Fly
Roves Beetle Humpback Fly
Cheese Fly Screw Worm Fly Scavenger Fly
Active Decay
Blow Fly
Flesh Fly
House Fly
Rove’s Beetle Cheese Fly Carrion Beetles
Advanced Decay
Roves Beetle
Checkered Beetles
Dried Remains
Picnic Beetle
Cheese Fly
Dermestid Beetle
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.
Classification of a House Fly
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Kingdom - Animal
Phylum - Arthropods
Class - Insects
Order - Diptera (All Flies)
Family - Muscidae
Genus - Musca
Species - domestica
Musca domestica
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
Another Look
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.
Another look at eggs
Larva
• Molt (shed their
skin) twice after
hatching
• Breath through
anterior and
posterior slits
called spiracles
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.
Spiracles are distinct
• Different species of fly larva have
different spiracle characteristics
Peritreme
Spiracular
Slits
Identifying Maggots by
Spiracular Slits
• Maggots can be
identified by their
distinguishing
spiracular slits.
Pupa
• Once larva mature they stop eating and
metamorphose into an adult fly.
Basic Anatomy of an Adult Fly
• Insects have three
body parts
– Head
– Thorax
– Abdomen
• Six Legs
• Wings