Transcript Forensic Entomology - Mount Mansfield Union High School

Forensic Entomology
The Study of the Insects
Associated with a Dead Body…
Why Are Insects Used in Forensic
Science?
• In most seasons and environments,
insects colonize a dead body almost
immediately after death
• Their rate of development and species
dynamics over time can be used to
accurately determine time since death.
• After 72 hours, entomological evidence
is the most accurate method to
determine the elapsed time since death.
The History of Forensic
Entomology
• 1st recorded use: 13th century China
• Became quite commonly used in Europe
throughout the 20th century
• Popularity increased in North America in
the 1970’s
• Today: used quite extensively and
commonly in homicide investigations.
What Can Insects Tell you?
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Post mortem interval
Whether the body was moved after death
Whether the body was disturbed
Presence and position of wound sites
If the victim used drugs or was poisoned
Length of time of abuse or neglect in living
victims
Determination of Elapsed Time
Since Death
Two Methods:
• Method #1: Blowflies are attracted to a
body immediately following death
– Dipteran Larval Development follows the
progression of several stages of insect life on the
body
– Predictable, linear pattern of development (at
optimum temperatures)
– Entomologist must identify all types of insects on
body, temperature at crime scene over elapsed time,
what stages of life the specimen have already
completed, and any published data on species of
insects relevant to case.
Determination of Elapsed Time
Since Death (cont’d)
• Method #2: Successional
Colonization of Body
– As a body decomposes, it attracts
different insects
– Entomologist identifies all species of
insects that have been present on body
and reconstructs timeline.
Determining Whether the Body
Has Been Moved
• Insects can lay eggs on body at original
scene and go unnoticed by killer.
• Some insects live in only rural or urban
settings, and their presence on body proves
body has been moved from original location.
Body Disturbance
• Killers often return to body, and if body
has been disturbed the insects have
also been disturbed.
• Entomologists can time since death
and when the body was disturbed
• Disturbance timeline can help link
suspects back to crime.
Presence and Position of
Wounds
• Blow Flies lay eggs as close to wounds
as possible on body.
• In advanced decomposition, atypical or
irregular colonization patterns can
indicate wound sites.
• Forensic Pathologist must be called in
to identify a wound and what weapon
caused it.
Linking Suspect to Scene
• Based on Locard’s Principle of
Exchange.
• Criminals often take entomological
evidence from scene.
• Types of insect bites on suspect can
prove presence at certain location.
• Insects found on suspect can carry
DNA or specific traits that match back
to insects on victim or crime scene.
Drugs
• Insects feeding on human tissue
absorb any unnatural substances like
drugs and poisons.
• If toxicology on victim does not work,
analysis of insects can identify toxin.
• Drugs can impact insect development
by speeding it up or slowing it down.
• Toxins digested by Blow Fly are
retained through all life stages.
Human and Animal Neglect or
Abuse
• Insects living on a living human or
animal do no damage, but help to clean
wounds.
• Presence of insects can show the
length of abuse or neglect.
• If insects colonized while victim was
alive, it is difficult to tell after death.
Challenges to Forensic
Entomology
• Temperature: Need temperature data to
get a precise idea of insect
development speed
• Season: Forensic entomology is only
valuable during certain times of the
year, when insects are present
• Exclusion of Insects: Freezing, burying
or wrapping a body can prevent insects
from colonizing it.