Entomology

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Entomology
Introduction
o Entomology is the study of
insects
o Forensic entomology is the study
of the insects associated with a
dead body
o Also known as medicolegal
o Forensic entomologists are called
into homicide investigations when
time of death is unknown and their
evidence is usually presented in
court as expert testimony
Introduction
o Insects begin colonizing at a
dead body immediately after
death
o Dependent on season and
environment
o Rate of development of the
species can be used to estimate
time since death
o Can give an estimate up to a year
Introduction
o Entomological evidence is the
most accurate and frequently
the only method available to
determine the elapsed time
since death
o Due to rigor, algor, and livor mortis
being useless after 72 hours
Introduction
o Insects are also used to
o Determine whether the body has
been moved after death
o Determine whether it has been
disturbed
o Determine the presence or position
of wound sites
o Determine whether the victim used
drugs or was poisoned
o Determine the length of time of
neglect or abuse in living victims
Importance of Determining Time Since Death
o Important for the family of the
deceased
o Understanding how, when, and why
a person has died can help to give
closure to family and friends and
allow them to move on with their
lives
Importance of Determining Time Since Death
o Timing of death may also have
legal implications
o Insurance policies
oWhether death occurred before or
after insurance coverage began
oImportant for families when money is
involved
Importance of Determining Time Since Death
o May indicate the length of time
that a fraud has occurred
o Receiving monies for family
members while family members
are deceased
History of Entomology
o Is one of the oldest forensic sciences
used in death investigations
o First recorded use was in 13th century
China
o Modern use of entomology in criminal
investigations began in France in the
mid 1800s
o First reported use of forensic
entomology in North America was in
Quebec in 1897
o Did not become common until 1970s
History of Entomology
o American Board of Entomology
was established in 1996 by Dr.
Paul Catts and Dr. Lee Goff
o European Association of Forensic
Entomology was established in
2001
Training
o Must have extensive training in
entomology
o Bachelors degree in biology, zoology, or
entomology
o Masters in entomology
o PhD in forensic entomology, insect
ecology, and taxonomy
o Board certification requires 5 years of
experience after PhD
o Most forensic entomologists are
university professors
Employment
o Forensic entomologists do not
work full time for crime labs
o Primary employment is in research
and teaching
o Therefore, most have little or NO
experience with crime scenes,
legal report writings, or court
testimonies
Decomposition
o Begins at the moment of death,
caused by two factors
o Autolysis
oThe breaking down of tissues by the
body's own internal chemicals and
enzymes
o Putrefaction
oThe breakdown of tissues by bacteria
oThese processes release gases that
are the chief source of the
characteristic odor of dead bodies
o These gases swell the body
Decomposition
o Scavengers play an important role in
decomposition
o Insects and other animals are typically the
next agent of decomposition, if the body is
accessible to them
o The most important insects that are typically
involved in the process include the fleshflies
(Sarcophagidae) and blowflies
(Calliphoridae)
o The green-bottle fly seen in the summer is a
blowfly
o Larger scavengers, including coyotes, dogs,
wolves, foxes, rats, and mice may eat a
body if it is accessible to them
o Some of these animals also remove and scatter
bones.
Factors Involved in Decomposition
o In a roughly descending degree of
importance, those factors include:
o
o
o
o
o
o
o
o
o
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o
o
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Temperature
The availability of oxygen
Prior embalming
Cause of death
Access by insects
Burial, and depth of burial
Access by scavengers
Trauma, including wounds and crushing blows
Humidity, or dryness
Rainfall
Body size and weight
Clothing
The surface on which the body rests
Determination of Elapsed Time Since Death
o First method based on the
predictable development of
larval Diptera, known as the blow
fly
o Used from the first time the first egg
is laid on the remains until the first
adult flies emerge from the pupal
cases and leave the body
oEvidence valuable from a few hours to
several weeks after death
Determination of Elapsed Time Since Death
o Second method is based on the
predictable, successional
colonization of the body by a
sequence of carrion insects
o Can be used from a few weeks
after death until nothing but dry
bones remain
Blow Flies
o Blow flies are the first flies to be
attracted to a body
o They are large, metallic flies seen
near food or garbage cans in
summer
o Blow flies belong to the family
Calliphoridae, in the order
Diptera or “true flies”
Blow Flies
o Male and female blow flies
require a protein meal before the
ovaries and testes develop and
oogenesis and spermatogenesis
can occur
o Adult feeding may occur at the
dead body
o Majority of the flies attracted to
remains are females searching for
egg laying sites
Blow Flies
o Blow flies develop from eggs
through the first, second, and
third instar stages, and then the
pupal stage before becoming
adults
o Stages influenced by species of
blow flies and temperature of
surroundings
Blow Flies
o Insects are cold-blooded so their
development is temperature
dependent
o As temperature increases, they
develop more rapidly
o As temperature decreases, they
develop more slowly
Blow Flies
o Analysis of the oldest insect
stage on they body, together
with knowledge of the
meteorological conditions at the
scene, can be used to determine
how long insects have been
feeding on the body, and hence,
how long the victim has been
dead
First Instar Stage
o Once blow fly eggs have been laid,
they will hatch into first instar larvae
o Larvae rely on protein for their meals
o Females lay eggs on open wounds of
dead individuals or around orifices of a
living individual
o Face is colonized before other areas
because the skin is easier to penetrate
oExcept in the case of rape cases, flies
attracted to genetalia
Second Instar Stage
o First instar larvae shed larval
cuticle and mouthparts when
entering second instar stage
o Is more capable of penetrating the
skin than the first instar larvae
oDoes so with proteolytic enzymes
Third Instar Stage
o Third instar stage begins with second
instar larvae shedding its cuticle
o Are called maggots
o Maggots aggregate together in large
masses
o Can remove a large amount of tissue
in a very short amount of time
o After feeding, the maggots move on
to a site where they can pupate
o Remove outer cuticle so they can
emerge as a fly
Time Span
o Female lays 2,000 eggs in her
lifetime
o Once eggs are laid, they hatch
between 12 and 48 hours
o It takes 14 days for the fly to
emerge from the pupal case
Factors Used to Determine Time Since Death
o 4 factors must be taken into account
o Oldest stage of blow fly associated with
the body
o Look at old pupal cases
o Species of insects
o Each species develop at different rates so
each species of insects at the scene need to
be collected
o Temperature data
o Must be able to determine temperature of
crime scene for a period of time
o Developmental data
o Must know how fast or how slow the specific
species develop
Determining Whether the Body has been Moved
o Insects present on the deceased
body that are not prevalent to
the crime scene can indicate
that the victim was murdered
elsewhere and was dumped at
another location
Presence and Position of Wounds
o Insects are attracted first and
foremost to wounds so the first
instar larvae will have access to
liquid protein for nutrition
o Wound sites in individuals that
have completely decomposed
are shown by irregular or
atypical insect colonization
Linking Suspect to Scene
o Sometimes, criminals carry
entomological evidence on
them unknowingly
o This evidence can place them at
the crime scene by examining
the life cycles of the insects
Drugs
o Insects that feed on the body of
individuals that have been
poisoned can be examined to
determine what type of drug or
toxin the person was poisoned
with
o It is important to note that specific
drugs either speed up or slow down
larval development
oCan influence entomologist’s final
report
Collection of Entomological Evidence
o Evidence should be collected by
an entomologist
o If not available, a police death
investigator should collect the
evidence
o Different stages of larval growth
should be collected and bagged
separately
o Sample of soil should also be
collected from just outside the
area marked by body fluids
Challenges to Forensic Entomology
o 3 challenges exist
o Temperature
oTemperature of crime scene and the
temperature that the insects have
been exposed to us unknown
o Season
oEntomology is valuable only in spring,
summer, and fall
o Exclusion of insects
oInsects are excluded based on
condition of body
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