Download Processing a Crime Scene for Insect Evidence 23

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Forensic Science: Fundamentals & Investigations, 2e
Chapter 11
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Chapter 11 Forensic Entomology
By the end of this chapter you will be able to:
11.1 Describe several examples of the ways that forensic
entomology is used to help solve crimes.
11.2 Compare and contrast the four stages of blowfly
metamorphosis, and describe the significance of blowflies in
forensic entomology.
11.3 Describe the function of each of the following organs
on blowflies and explain the significance of each structure to
forensic entomology: spiracles, mouth hooks, crop.
11.4 Describe the effect of different environmental factors on
insect development.
11.5 Describe the five stages of decomposition.
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Forensic Science: Fundamentals & Investigations, 2e
Chapter 11
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Cengage/NGL/South-Western © 2016
Chapter 11 Forensic Entomology
By the end of this chapter you will be able to:
11.6 Relate the process of insect succession to the
changing environment that occurs during the stages of
decomposition.
11.7 Explain how forensic entomologists interpret forensic
evidence and environmental conditions to estimate a
postmortem interval.
11.8 Explain how insect evidence is analyzed to provide
evidence of the deceased person’s identity or drug, poison,
or toxin exposure.
11.9 Summarize the procedures for documenting and
collecting insect evidence from a crime scene.
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Chapter 11
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Chapter 11
Vocabulary
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accumulated
degree hours (ADH)
complete
metamorphosis
crop
entomology
forensic entomology
grub
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Forensic Science: Fundamentals & Investigations, 2e
Chapter 11
insect succession
instar
larva
maggot
oviposition
pupa
spiracles
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Introduction
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Insects have 3
body segments:
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Head
Thorax
Abdomen
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Introduction (continued)
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Forensic entomology
uses insect evidence
in civil and criminal
investigations.
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Adults
Nymphs
Pupae
Larvae
Eggs
Insect body parts
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How is Forensic Entomology
Used?
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Insect evidence can be
used to:
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Locate a body
Determine if the body
was moved
Identify a geographic
range of the crime
Link a suspect to a crime
Indicate where a suspect
had been traveling
Trace the origin of drugs
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Chapter 11
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Forensic Entomologists
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Forensic entomologists may answer the
following questions:
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Where on the body were the injuries?
Was the body moved after death?
Was the victim restrained while alive?
Was the body covered, buried, or submerged in
water?
Was the deceased exposed to any toxic chemical
or under the influence of recreational drugs?
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History of Forensic
Entomology
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In 1247, The Washing Away of Wrongs
describes how flies were used to identify a
bloody murderer.
In 1855, insect evidence was used to solve the
death of a murdered infant hidden in the wall of
a house.
In the early part of the 20th century, research
done on the effect screwworm flies had on living
cattle and sheep laid the groundwork for future
entomologists.
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Insects and Decomposition
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A decomposing body follows a regular pattern and
predictable changing habitats. The stages include:
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Fresh
Bloated
Decay
Active decay
Dry, or skeletal, decay
These different habitats support the predictable
sequence of insect succession on a dead body.
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Chapter 11
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Blowflies (Bottle Flies)
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When putrescine and
cadaverine are released by
decomposing tissue,
blowflies are alerted to
potential locations to lay
their eggs.
After feasting on the
protein-rich fluids from a
decomposing body, female
flies deposit their eggs in
clusters on the body.
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Growth and Development
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During the complete
metamorphosis of
blow flies, the
following stages
occur:
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Egg
Larva
Pupa
Adult
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Morphology (Body Shape)
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Blowfly larvae use
hooks to dig and
scrape at
decomposing flesh
to move the flesh
toward the mouth.
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Morphology (Body Shape)
(continued)
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Spiracle configuration alerts investigators to
the developmental stage of the instar.
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Morphology (Body Shape)
(continued)
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An empty pupal case signals that a body
has been in an area long enough for the
blowfly to complete its full lifecycle.
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Houseflies, Flesh Flies,
and Coffin Flies
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Beatles and Other Insects of
Decomposition
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Beetles follow a predictable path of insect
succession on a decomposing body.
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Estimating Postmortem Interval
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Blowfly Importance
Factors Affecting Development
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Degree Hours
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Temperatures and environmental conditions
Accumulated degree hours (ADH) is the number
of hours at an adjusted average Celsius
temperature than it takes an insect species to
reach a particular stage of development.
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Processing a Crime Scene for
Insect Evidence
1. Death-Scene observations
2. Collection of Meteorological Data
3. Two Collections: Collect live
insects, and collect and preserve
other insects from the body at the
crime scene.
4. After Body Removal: Collect
insects from the surrounding soil.
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Summary
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Insects, the most numerous of all animals, provide valuable
evidence in solving crimes.
Forensic entomology is used to estimate postmortem
intervals, identify the geographic location of the crime scene,
link a suspect to a victim or crime scene, determine if a body
was moved, locate injury sites, determine exposure to drugs
or toxins, and provide evidence of neglect or abuse.
The five stages of decomposition include fresh, bloated,
active decay, advanced decay, and dry decay; stages of
decomposition cause predictable changes in the chemical
and physical environment of a body and the area
surrounding it.
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Summary (continued)
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Forensic insects include flies, beetles, wasps, ants,
and more. Insects follow a predictable sequence of
inhabiting a dead body, known as insect succession.
Blowflies, usually the first to inhabit a dead body,
undergo four stages of complete metamorphosis:
egg, larva (first instar, second instar, third instar),
pupa, and adult.
Larvae use mouth hooks to help ingest food and
move, a crop to store food, and spiracle slits to
breathe.
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Summary (continued)
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Beetles usually arrive after flies and may consume
the dead body or consume eggs and larvae found on
the body.
Variables affecting the rate of insect growth include
temperature, sun, shade, wind, moisture, injuries to
the deceased, and a body that is clothed or
wrapped. All must be considered when a forensic
entomologist interprets insect evidence.
The postmortem interval is an estimate of the
interval of time between when the body was found
and death.
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Summary (continued)
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Accumulated degree hours (ADH) are the
number of hours at an adjusted average
temperature it takes for an insect species to
develop to a given developmental stage. ADH
are used to estimate postmortem intervals.
Evidence collection includes crime-scene
observations, collection of live insects and eggs,
preserving insects, and collection of
meteorological data.
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