Transcript Forensic Entomology

Forensic Entomology
Critters on Cadavers
What do Forensic
Entomologists Do?
• Forensic Entomologists apply their knowledge of entomology
to provide information for criminal investigations.
• A forensic entomologist’s job may include:
– Identification of insects at various stages of their life cycle,
such as eggs, larva, and adults.
– Collection and preservation of insects as evidence.
– Determining an estimate for the postmortem interval or
PMI (the time between death and the discovery of the
body) using factors such as insect evidence, weather
conditions, location and condition of the body, etc.
– Testifying in court to explain insect-related evidence found
at a crime scene.
Cool Jobs:
Did you know? Maggots can be used to test a corpse
for the presence of poisons or drugs. Some drugs
can speed up or slow down the insect’s development
Forensic
Entomology
Discovery
Video
Insects as Evidence
• Most insects used in investigations are in two major orders:
1 – Flies (Diptera) and
2 – Beetles (Coleoptera)
• Species succession may also provide clues for investigators.
Some species may to feed on a fresh corpse, while another
species may prefer to feed on one that has been dead for two
weeks. Investigators will also find other insect species that
prey on the insects feeding on the corpse.
Five Stages of Decomposition Fueled by
Insect Activity.
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Fresh
Bloat
Decay
Post-decay
Dry (skeletal)
Fresh
• Begins at death
• Flies begin to arrive
• Temperature falls to
that of the ambient
temperature.
• Autolysis, the
degradation of
complex protein and
carbohydrate
molecules, occurs.
Bloat
• Swells due to
gases
produced by
bacteria
• Temperature
rise of the
corpse
• Flies still
present
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.
• The corpse is reduced to at least ten
percent of the original mass.
• In the last stage (Skeletal Stage), only
bone and hair remain.
Insects as Evidence
• Weather data is also an important tool in analyzing insect
evidence from a corpse. Investigators will make note of the
temperature of the air, ground surface, the interface area between
the body and the ground, and the soil under the body as well as
the temperature inside any maggot masses. They will also collect
weather data related to daily temperature (highs/lows) and
precipitation for a period of time before the body was discovered
to the time the insect evidence was collected.
• Other factors that might affect their PMI estimates:
– Was the body enclosed in an area or wrapped in a material that would have
prevented flies from finding the corpse and laying eggs?
– Were other insect species present that may have affected the development of
the collected species?
– Were there drugs or other poisons in or on the body that might have
– affected the larvae’s development?
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Did you know…
The “Body Farm” in Knoxville, Tennessee is a university research facility
to investigate human decomposition under various conditions in order to
understand the factors which affect its rate.
Click the image to view a video about the Body Farm!
Decay Rates Are Variable
• Studies of decay rates of 150 human
corpses at in the Anthropological Facility in
Tennessee (The Body Farm)
• Most important environment factors in
corpse decay:
• Temperature
• Access by insects
• Depth of burial
• Other Factors
• Chemical-- embalming agent, insecticides, lime,
etc.
• Animals disrupting the corpse
Time of Death can be broadly
estimated up to about 36 hours
Temperature
Stiffness
Time of death
Warm
Not stiff
Dead less
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
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
Phylum Arthropoda
• 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!
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
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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.
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.
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 a silent
witnesses.
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, elongate, whitish to
yellowish
• 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.
Blow Fly Metamorphosis
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1st – Adult flies lay eggs on the
carcass especially at wound areas or
around the openings in the body such
as the nose, eyes, ears, anus, etc.
2nd – Eggs hatch into larva
(maggots) in 12-24 hours.
3rd– Larvae continue to grow and
molt (shed their exoskeletons) as
they pass through the various instar
stages.
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1st Instar - 5 mm long after 1.8 days
2nd Instar - 10 mm long after 2.5 days
3rd Instar – 14-16 mm long after 4-5
days
4th – The larvae (17 mm) develop
into pupa after burrowing in
surrounding soil.
5th – Adult flies emerge from pupa
cases after 6-8 days.
Adult
pupa
eggs
1st
instar
larva
3rd instar
larva
2nd instar
larva
It takes approximately 14-16
days from egg to adult depending
on the temperatures and
humidity levels at the location of
the body.
Postmortem Interval (PMI)
• Entomological evidence collection can
be done in a variety of ways:
– Identify the species
– Document larvae length
– Determine the instar
– Determine postmortem interval estimation
• Depending on species- 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.
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
Examples of Diptera (Flies)
• Early Stage Decomposition
Blow & Greenbottle Flies(Calliphoridae)
Metallic thorax and abdomen
Life Cycle of a Calliphoridae Fly
• Late Stage Decomposition
House Fly
(Muscidae)
Cheese Skipper
(Piophilidae)
Flesh Fly
(Sarcophagidae)
Striped thorax
F.E. 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)
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 morale 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.