What information can a forensic entomologist provide at
the death scene?
Forensic entomologists are commonly called upon to
determine the postmortem interval or "time since death" in homicide
investigations. More specifically, the forensic
entomologist estimates a portion of the postmortem interval based on the
age of the insect present. This entomological based estimation is
most commonly called the "Time Since Colonization". Based on the
factors in a particular investigation, this may, or may not, closely
approximate the entire postmortem interval. In either case, it is
the duty of the Forensic Pathologist, Medical Examiner, or Coroner to
estimate the postmortem interval, and the Forensic Entomologist may
assist them in providing information on the "time since colonization",
which can ultimately be used to substantiate a portion of the postmortem
interval.
The forensic entomologist can use a number of
different techniques including species succession, larval weight, larval
length, and a more technical method known as the accumulated degree hour
technique which can be very precise if the necessary data is available.
A qualified forensic entomologist can also make inferences as to
possible postmortem movement of a corpse. Some flies prefer
specific habitats such as a distinct preference for laying their eggs in
an outdoor or indoor environment. Flies can also exhibit
preferences for carcasses in shade or sunlit conditions of the outdoor
environment. Therefore, a corpse that is recovered indoors with
the eggs or larvae of flies that typically inhabit sunny outdoor
locations would indicate that someone returned to the scene of the crime
to move and attempt to conceal the body.
Similarly, freezing or wrapping of the body may be indicated by an altered species
succession of insects on the body. Anything that may have prevented the insects from
laying eggs in their normal time frame will alter both the sequence of species and their
typical colonization time. This alteration of the normal insect succession and fauna
should be noticeable to the forensic entomologists if they are familiar with what would
normally be recovered from a body in a particular environmental habitat or geographical
location. 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 otherwise helpless) often have
associated fecal and urine soaked clothes or bed dressings. Such material will
attract certain species of flies that otherwise would not be recovered. Their
presence can yield many clues to both antemortem and postmortem circumstances of the
crime. Currently, 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 suspects at a known location within a definable period of time and recovery of
the victims' blood can also create a link between perpetrator and suspect.
The insects recovered from decomposing human remains can be a valuable tool for
toxicological analysis. The voracious appetite of the insects on corpses can quickly
skeletonize the remains. In a short period of time the fluids (blood and urine) and
soft tissues needed for toxicological analysis disappear. However, it is possible to
recover the insect larvae and run standard toxicological analyses on them as you would
human tissue. Toxicological analysis can be successful on insect larvae because
their tissues assimilate drugs and toxins that accumulated in human tissue prior to death.
For a complete listing of the Diplomates and
Members of the American Board of Forensic Entomology (Click
Here.)
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