Download Forensic Entomology - the Redhill Academy

Forensic
Entomology
a word derived from the Greek words
entomon (an insect) and logos (science).
What can it do at a crime
scene?
Forensic Entomology can determine…
• How long the person has been dead (also
known as the post-mortem interval or PMI)
• Whether the body has been moved after
death
• What injuries they may have sustained
Invertebrates attracted to dead bodies
• A dead body attracts a wide variety of insects which use the
corpse for food and as a place to lay their eggs.
• Flies usually arrive first to a corpse, particularly the blowflies
and flesh flies (sometimes within minutes of death).
• The eggs laid by these flies, and the larvae that subsequently
hatch and grow on the corpse, can be used to give a minimum
PMI (the shortest amount of time the person can have been
dead in order to achieve the observed insect community)
If investigators find larvae that take at
least three days to develop, they can
infer that the victim has been dead for
at least three days.
Observation & identification of
correct species
• It is very important that careful observations of
invertebrate species around the corpse are made
and recorded for identification purposes.
• Quick task…you will see an image shortly which you will
have to memorise. You will get 1 minute to observe the
image and a further minute to record your recollections
afterwards.
The blowfly lifecycle
Growth rate for
flies is
dependent on
temperature.
To estimate the
PMI, an
investigator must
know the
temperature
around the body
for the period in
question.
Times given in
this chart are for
70°F.
The blowfly lifecycle
• Adult female blow flies arrive within minutes to lay eggs
on a cadaver. Each deposits about 250 eggs in the natural
openings of the body and open wounds.
• The eggs hatch into first-stage maggots within 24 hours.
• These feed and then moult into second-stage maggots,
which feed for several hours, and then moult into thirdstage maggots.
• After more feeding, the third-stage maggots move away
from the body and metamorphose into adult flies.
Insect succession
• The principle of insect succession can be used to
estimate the PMI.
• Different species of insects prefer different stages of
decomposition.
• As the body decays further, it becomes less favourable
to early colonisers and more desirable to other species.
WARNING!
Many factors can influence the rate of succession and
decomposition including ambient temperature, time of day,
season and the situation of the body (eg. covered,
submerged, whether located near another corpse…etc)