Entomology

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Entomology
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Introduction

• Entomology is the study of insects
• Forensic entomology is the study of the insects
  associated with a dead body
• Also known as medicolegal
• Forensic entomologists are called into homicide
  investigations when time of death is unknown and
  their evidence is usually presented in court as
  expert testimony

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Introduction

• Insects begin colonizing at a dead body
  immediately after death
• Dependent on season and environment
• Rate of development of the species can be used to
  estimate time since death
• Can give an estimate up to a year

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Introduction

• Entomological evidence is the most accurate and
  frequently the only method available to determine
  the elapsed time since death
• Due to rigor, algor, and livor mortis being
  useless after 72 hours

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Introduction

• Insects are also used to
• Determine whether the body has been moved after
  death
• Determine whether it has been disturbed
• Determine the presence or position of wound sites
• Determine whether the victim used drugs or was
  poisoned
• Determine the length of time of neglect or abuse
  in living victims

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Importance of Determining Time Since Death

• Important for the family of the deceased
• 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

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Importance of Determining Time Since Death

• Timing of death may also have legal implications
• Insurance policies
• Whether death occurred before or after insurance
  coverage began
• Important for families when money is involved

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Importance of Determining Time Since Death

• May indicate the length of time that a fraud has
  occurred
• Receiving monies for family members while family
  members are deceased

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History of Entomology

• Is one of the oldest forensic sciences used in
  death investigations
• First recorded use was in 13th century China
• Modern use of entomology in criminal
  investigations began in France in the mid 1800s
• First reported use of forensic entomology in
  North America was in Quebec in 1897
• Did not become common until 1970s

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History of Entomology

• American Board of Entomology was established in
  1996 by Dr. Paul Catts and Dr. Lee Goff
• European Association of Forensic Entomology was
  established in 2001

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Training

• Must have extensive training in entomology
• Bachelors degree in biology, zoology, or
  entomology
• Masters in entomology
• PhD in forensic entomology, insect ecology, and
  taxonomy
• Board certification requires 5 years of
  experience after PhD
• Most forensic entomologists are university
  professors

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Employment

• Forensic entomologists do not work full time for
  crime labs
• Primary employment is in research and teaching
• Therefore, most have little or NO experience with
  crime scenes, legal report writings, or court
  testimonies

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Decomposition

• Begins at the moment of death, caused by two
  factors
• Autolysis
• The breaking down of tissues by the body's own
  internal chemicals and enzymes
• Putrefaction
• The breakdown of tissues by bacteria
• These processes release gases that are the chief
  source of the characteristic odor of dead bodies
• These gases swell the body

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Decomposition

• Scavengers play an important role in
  decomposition
• Insects and other animals are typically the next
  agent of decomposition, if the body is accessible
  to them
• The most important insects that are typically
  involved in the process include the fleshflies
  (Sarcophagidae) and blowflies (Calliphoridae)
• The green-bottle fly seen in the summer is a
  blowfly
• Larger scavengers, including coyotes, dogs,
  wolves, foxes, rats, and mice may eat a body if
  it is accessible to them
• Some of these animals also remove and scatter
  bones.

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Factors Involved in Decomposition

• In a roughly descending degree of importance,
  those factors include
• 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

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Determination of Elapsed Time Since Death

• First method based on the predictable development
  of larval Diptera, known as the blow fly
• 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
• Evidence valuable from a few hours to several
  weeks after death

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Determination of Elapsed Time Since Death

• Second method is based on the predictable,
  successional colonization of the body by a
  sequence of carrion insects
• Can be used from a few weeks after death until
  nothing but dry bones remain

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Blow Flies

• Blow flies are the first flies to be attracted to
  a body
• They are large, metallic flies seen near food or
  garbage cans in summer
• Blow flies belong to the family Calliphoridae, in
  the order Diptera or true flies

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Blow Flies

• Male and female blow flies require a protein meal
  before the ovaries and testes develop and
  oogenesis and spermatogenesis can occur
• Adult feeding may occur at the dead body
• Majority of the flies attracted to remains are
  females searching for egg laying sites

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Blow Flies

• Blow flies develop from eggs through the first,
  second, and third instar stages, and then the
  pupal stage before becoming adults
• Stages influenced by species of blow flies and
  temperature of surroundings

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Blow Flies

• Insects are cold-blooded so their development is
  temperature dependent
• As temperature increases, they develop more
  rapidly
• As temperature decreases, they develop more
  slowly

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Blow Flies

• 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

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First Instar Stage

• Once blow fly eggs have been laid, they will
  hatch into first instar larvae
• Larvae rely on protein for their meals
• Females lay eggs on open wounds of dead
  individuals or around orifices of a living
  individual
• Face is colonized before other areas because the
  skin is easier to penetrate
• Except in the case of rape cases, flies attracted
  to genetalia

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Second Instar Stage

• First instar larvae shed larval cuticle and
  mouthparts when entering second instar stage
• Is more capable of penetrating the skin than the
  first instar larvae
• Does so with proteolytic enzymes

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Third Instar Stage

• Third instar stage begins with second instar
  larvae shedding its cuticle
• Are called maggots
• Maggots aggregate together in large masses
• Can remove a large amount of tissue in a very
  short amount of time
• After feeding, the maggots move on to a site
  where they can pupate
• Remove outer cuticle so they can emerge as a fly

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Time Span

• Female lays 2,000 eggs in her lifetime
• Once eggs are laid, they hatch between 12 and 48
  hours
• It takes 14 days for the fly to emerge from the
  pupal case

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Factors Used to Determine Time Since Death

• 4 factors must be taken into account
• Oldest stage of blow fly associated with the body
• Look at old pupal cases
• Species of insects
• Each species develop at different rates so each
  species of insects at the scene need to be
  collected
• Temperature data
• Must be able to determine temperature of crime
  scene for a period of time
• Developmental data
• Must know how fast or how slow the specific
  species develop

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Determining Whether the Body has been Moved

• 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

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Presence and Position of Wounds

• Insects are attracted first and foremost to
  wounds so the first instar larvae will have
  access to liquid protein for nutrition
• Wound sites in individuals that have completely
  decomposed are shown by irregular or atypical
  insect colonization

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Linking Suspect to Scene

• Sometimes, criminals carry entomological evidence
  on them unknowingly
• This evidence can place them at the crime scene
  by examining the life cycles of the insects

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Drugs

• 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
• It is important to note that specific drugs
  either speed up or slow down larval development
• Can influence entomologists final report

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Collection of Entomological Evidence

• Evidence should be collected by an entomologist
• If not available, a police death investigator
  should collect the evidence
• Different stages of larval growth should be
  collected and bagged separately
• Sample of soil should also be collected from just
  outside the area marked by body fluids

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Challenges to Forensic Entomology

• 3 challenges exist
• Temperature
• Temperature of crime scene and the temperature
  that the insects have been exposed to us unknown
• Season
• Entomology is valuable only in spring, summer,
  and fall
• Exclusion of insects
• Insects are excluded based on condition of body