Forensic Entomology
Insects in the Forensic Sciences
What is Forensic Entomology?
• The application of insects and other
arthropods to legal issues and court
proceedings
What is it used for?
• Applications
– Estimation of time of death
– Cases involving possible sudden death
– Traffic accidents with no immediately
obvious cause
– Possible criminal use of insects
How does FE work?
• Fact – insects feed on humans after
death. Yup – not good news, but we
are part of the cycle of life!
• If insects are found on a corpse, the
life stage of the insect can be used to
determine time of death
– This calculation is known as the
POSTMORTEM INTERVAL (PMI)
PMI Conditions
PMI must take into consideration many
environmental variables
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Temperature
Time of day death occurred
Time of year death occurred
Whether the corpse is submerged in soil or
water.
Divisions of Forensic Science
• Urban – Relates insects to human
structures and environments
• Stored Products – Insect infestations
of stored food and beverages
• Mediocriminal – The only division that
has a criminal aspect. Relates to
insects feeding on human tissue in the
postmortem period.
After Death
• As the body decays, odors attract insects to
the dead body. Levels of putricine (decomp.
enzyme,) sulfur and methane compounds
send up an “open for dinner” flare.
• The flies (order Diptera) are the first to
arrive. Blowflies (F. Calliphoridae) and flesh
flies (F. Sarcophagidae) are flesh feeders
and will be the first in line.
• Flies can arrive within minutes or up to a
couple hours after death.
• In many cases flies arrive before the
completion of a crime and are silent
witnesses.
Phylum Athropoda
• Not as large of a biomass as bacteria – but
run a respectable second!
• Unifying Characteristic – hard exoskeleton
• Class Insecta includes bees and wasps
(Order Hymenoptera,) flies (O. Diptera,)
butterflies (O. Lepidoptera,) dragonflies (O.
Odanata,) beetles (O. Coleoptera,) etc.
• “True Bugs” are Order Hemiptora. No
hemiptorans have any consequence for
forensic science – so erase “bugs” from your
vocabulary!
Fly Life Cycle
• If no trauma is present on the body, female
blowflies will lay eggs in exposed body
openings (ears, nose, mouth, anus,
genitalia.)
• Flesh flies don’t lay eggs, they deposit
larvae.
• The colonization pattern is due to the mouth
parts of adult flies.
– Blowflies and flesh flies have spongy mouth
parts. They lack piercing apparatus that can cut
through unbroken human skin. The body
openings provide a moist, warm environment for
larvae development.
Blowflies
Blowfly Classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Uniramia
Class: Insecta
Order: Diptera
Family: Calliphoridae
Blowfly Eggs
• Small, 2-3 mm length, elongated shape,
white to yellow color
• Found in large clusters in and around body
openings as well as injuries
• Clearly visible to naked eye
• Colder months may see fewer in numbers
• Can be found in more hidden locations such
as under eyelids or in nostrils
• Eggs typically hatch within hours but may
take up to 2-3 days depending on conditions
Blowfly Larvae
• One fairly small and featureless larvae
hatches from each egg
• The body tapers from anterior to
posterior – Mouth at the anterior,
spiracles at the posterior
• Posterior contains breathing apparatus
called spiracles
– Spiracles, along with body size and
shape provide important info for
identification
Blowfly larvae
• Large numbers of blowfly
typically hatch at a time and
remain together while they
feed on a corpse
• These maggot masses
generally form in the head
region and move down the
torso as they feed.
• As they feed the larvae
secrete digestive enzymes
which allows them to
consume nearly all the soft
tissue on the corpse
Blowfly life cycle
• Blowfly larvae go through three instars
(molts)
• They are considered fully grown at the
third instar
• This can occur in several days or
several weeks depending on species,
environmental conditions and number
of larvae present
Pupa Stage
• After the 3rd instar
larvae go through a
drastic behavioral
change
– they crawl away from the
corpse and burrow down
into the soil to transform
into the pupal stage and
complete the life cycle
Pupa
• The pupa form when the outer larval skin
hardens and shrinks
• Inside this “case” the adult blowfly will form
• Once the adult fly emerges, the pupal case
does not decompose. It can remain under a
corpse for hundreds of years
• Pupal cases can provide valuable forensic
info to investigators long after a crime has
been committed.
Postmortem Interval (PMI)
• Entomological evidence collection can
be done in a variety of ways
• For our purpose we will:
– Identify the species
– Document larvae length
– Determine the instar
– Determine postmortem interval estimation
• Depending on species we will use
extrapolation of instar length or the
accumulated degree day theory
Post Mortem Intervals
• PMI – The use of insect life cycles to
estimate the time a corpse has been in
the location where it was found
• PMI does not DETERMINE the time of
death
– Time of death is established by the
medical examiner
• Forensic entomology can provide value
information for the M.E.
Forensic Applications
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Time of injury vs. death
Estimation of time of death
Whether or not a corpse has been moved
Instances of insects as weapons
Child and elderly abuse and neglect
Single vehicle car accidents (insect stings
and path vehicles have traveled)
• Aircraft crashes (instrument obstruction and
engine and fuel line clogging)
F.E. Applications – Blood Evidence
• “Roach Track” Confusion
– Roaches are notorious for confusing
blood spatter analysis
– Blood trajectory is often critical to forensic
investigations
– Roaches, silverfish and other household
insects often travel through bloodstained
areas
• “Roach tracks” frequently confuse forensic
investigators that are untrained in how to
identify them
Blood Spatter Confusion – Fleas and Flies
• Flies also track through blood, but “fly
specks” are a far greater problem for
investigators
• Flies ingest blood and can leave large
undigested droplets behind in previously
uncontaminated areas. These droplets can
enlarge a crime scene unneccessarily.
• Fleas also leave behind undigested blood in
their feces (commonly known as “flea dirt.”)
– Flea dirt in a heavily infested dwelling can falsely
suggest blood “evidence”
Roaches, Flies, Fleas
• It is becoming more clear that household
insect infestations need to be included as a
variable in forensic investigations
• Proper identification of household pests can
save valuable time and resources for
technicians and investigators
• Best for juries to hear about insect
“confusion” from CSI’s rather than from
attorneys for the defense!
Insects and Illegal Drugs
• Shipments of illegal drugs often
contain insect infestations, especially
cannabis and heroine (derived from
poppy plants.)
• Analysis of insect “stowaways” can
allow investigators to track country of
origin, and in many cases the local
area of cultivation.
• PMI used to detect illegal
drugs/poisons in fly larvae (consumed
from corpses)
The moral of the story…
• Insects are becoming invaluable in the
investigation of crime
• Forensic entomology is one of the
fastest growing specialties in forensic
science.
• All Crime Scene Investigation Units
MUST be prepared to include insect
collection, identification and analysis in
their investigations.