Download NOTES - FORENSIC ENTOMOLOGY Forensic Entomology is the

NOTES - FORENSIC ENTOMOLOGY
Forensic Entomology is the application of the knowledge of insect
activity in a criminal investigation, and legal context. The insects of
greatest value to forensic entomology are blowflies, family
Calliphoridae.
Necrophagus insects – consume dead flesh
 Flies
 Beetles – found when corpse is more decomposed
 Moths – feed on mammalian hair during larval stages – appear
later
 Wasps, ants, bees – final stages of decomposition – predatory
and feed on other insects.
Order of events after a death at an outdoor location:
 arrival of insects, such as the blow fly, almost immediately
 flies will begin colonizing the orifices and any wounds present on
the body of the recently deceased.
 Fly egg-laying sends a strong olfactory signal to other flies in the
area so a body can quickly become swarmed.
 Eggs are deposited continuously, producing young of varying
ages present at the same time.
 The most important specimen collected by a forensic
entomologist is the oldest stage present on the body.
o This specimen acts as a stopwatch that began the moment
the first egg was deposited.
o Using the species life cycle timetable with local
temperature and weather information, a forensic
entomologist is able to figure out PMI (post-mortem
interval). This entomological based estimation is most
commonly called the “time since colonization”.
The life cycle of a blow fly:
1. begins with oviposition (egg-laying)
2. development of the egg ends with an immature fly, called a larva
or maggot, hatching from the egg.
3. The larva sheds its skin 3 times during the larval phase.
4. The individual between each of the molts is called an instar. Thus,
there are 3 instars, each larger than the last. Each instar has a
different set of appendages.
5. Migration phase is next, where a larva stops feeding and travels
several feet away from the corpse. (this allows the larva to pupate
away from the environment of the body)
6. Pupation is marked by a hard shell the maggot secretes. It will
change from larval to adult stage. Some flies will remain as pupae
for days to weeks.
7. An adult fly emerges from the pupa and the cycle begins again.
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Most important environment factors in corpse decay:
• Temperature
• Access by insects
• Depth of burial
Necrophages - the first species feeding on corpse tissue. Includes
rue flies (Diptera) and beetles (Coleoptera).
Omnivores - species such as ants, wasps, and some beetles that
feed on both the corpse and associated maggots. Large populations
of omnivores may slow the rate of corpse’s decomposition by
reducing populations of necrophagous species.
Parasites and Predators - beetles, true flies and wasps that parasitize
immature flies.
Incidentals – pill bugs, spiders, mites, centipedes that use the corpse
as an extension of their normal habitat
The Life Cycle
 After eggs are laid, the duration of a typical blow fly life cycle is
dependent on the temperature. It requires a certain time period
(expressed as degree-days or degree-hours) for the larva to
develop.
 Degree days/hours are the number of days/hours multiplied by
the number of degrees above a threshold temp. for that species
(usually 50 degrees Fahrenheit).
o Below 50 degrees Fahrenheit does not count toward the
life cycle – it is too cold for the eggs/larvae/pupae to grow.
o At 70 degrees Fahrenheit: Eggs will hatch into larvae in
about 12 hrs; Larvae will pupate in about 12 days; and
adult flies will emerge from the puparia after approximately
8 more days. The complete life cycle will take 3 weeks.
o Drugs or poisons in the body can also affect the growth
rate of fly species.
 (Arsenic , a heavy metal found in rat poison, slows
down the growth rate of fly species).
 Narcotics like cocaine can accelerate the growth
rate, especially in the Calliphora vomitoria species.
 It is possible to recover the insect larvae and run
standard toxicology tests on them as you would
human tissue. The insects’ tissues assimilate drugs
and toxins that accumulated in human tissue prior to
death.
The stages of decomposition
5 Stages of decomposition fueled by insect activity
1. Fresh
2. Bloat
3. Decay
4. Post – decay
5. Dry (skeletal)
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Decomp. of a mammal begins at the “fresh” stage and progresses
until the body appears bloated. Flies arrive within minutes.
(commonly blow flies or flesh flies) .
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The bloated stage occurs because of the activity of bacteria which
produces gases inside the body. During this stage, house flies
(genus Musca) begin to appear and deposit eggs.
The decay stage begins with the splitting of the skin to allow
gases to escape.
By the end of the decay stage, the flesh is absent and only bone,
skin, and hair remain. The larvae begin their migration away from
the body to pupate.
In the post-decay stage, beetles begin to colonize the body and
consume the dry body.
Other important forensic clues:
 The complete absence of insects would suggest clues as to the
sequence of postmortem events as the body was probably either
frozen, sealed in a tightly closed container, or buried very deeply.
 Entomological evidence can also help determine the
circumstances of abuse and rape. Victims that are incapacitated
(bound, drugged, or helpless) often have associated fecal and
urine soaked clothes or bedding. Such material will attract certain
species of flies that otherwise would not be found.
 The location of the larval mass on a body can be important. If an
individual dies without sustaining a wound to the flesh (carbon
monoxide), then flies would initially lay eggs in the body orifices.
So larval mass is found in face/head and anal/genital regions first.
If the larval mass is found in the chest or abdomen, this indicates
an unnatural orifice, like a fatal stab wound in the trunk area.
 A corpse that is recovered indoors with the eggs or larvae of flies
that typically inhabit sunny outdoor locations would indicate that
the body had been moved (probably to conceal the body).
 It is now possible to use DNA technology not only to help
determine insect species, but to recover and identify the blood
meals taken by blood feeding insects. The DNA of human blood
can be recovered from the digestive tract of an insect that has fed
on an individual. The presence of their DNA within the insect can
place a suspect at the crime scene.
 Gunshot residue in the larval gut of an insect would indicate a
shooting when physical evidence no longer exists.