FORENSIC ENTOMOLOGY

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FORENSIC ENTOMOLOGY
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Entomology

• Entomology is the study of insects. Insects
  arrive at a decomposing body in a particular
  order and then complete their life cycle based on
  the surrounding temperature. By collecting and
  studying the types of insects found on a body, a
  forensic entomologist can predict the time of
  death.
• When one biological clock stops, others begin.
• --Neal Haskell, reknown forensic entomologist

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HISTORICALLY

• 1235 A.D., a Chinese death investigator named
  Sung Tzu wrote a book entitled The Washing Away
  of Wrongs. It contained one of the first accounts
  of the use of insects as forensic evidence. A
  murder, in which a sickle was used, occurred in a
  Chinese village.

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HISTORICALLY (cont)

• There were no suspects, so the investigator
  had all the men of the village stand in a line
  with their sickles on the ground in front of
  them. Flies landed on only one sickle--the one,
  that although cleaned, still had enough blood to
  attract the flies. The owner then confessed.

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Four Main Types of Species that Feed on Dead
Organisms

• Necrophages - feed directly on the corpse
• Flies (Diptera)
• Beetles (Coleoptera)
• Predators and Parasites attracted to organisms
  that are already feeding on the body
• Burying beetles (family Silphidae)
• Rove beetles (family Staphylinidae)
• Hister beetles (family Histeridae)
• Ants, bees, and wasps (Order of Hymenoptera)

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Four Main Types of Species that Feed on Dead
Organisms

• Species that feed on both the body and other
  arthropods
• Ants
• Wasps
• Some beetles
• Arthropods that use the corpse as an extension of
  their normal habitat
• Hunting spiders

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The First Species

• Flies are able to detect the smell of
  decomposition before humans. When a dead body is
  placed outside a blowfly will generally appear
  within ten minutes.

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The Blowfly

• Blowflies are one of the most common species on
  dead bodies.
• Blowflies have a shiny, metallic color so they
  are often called blue-bottle or green-bottle
  flies.
• They feed on any blood or fluids and then start
  laying eggs in and around the natural body
  cavities. The female can lay up to 250 eggs at
  one time.
• Once the food source is exhausted, they will prey
  on other species in the same genus (Chrysomya)
• Therefore, they act as both necrophages and
  predators.

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The Blowfly

• The eggs hatch within 23 hours. The maggots begin
  feeding on fluids leaking form the body. Later
  they enter openings on the body and feed on
  tissues.
• Other species of flies will begin to arrive and
  there will be competition for access to the
  corpse.
• The maggots are also a source of food for other
  insects.

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The maggots become a source of food for other
insects such as Beetles
Rove Beetle--Staphylinidae (Lathrobium
sp.)
Carrion Beetle--Silphidae (Nicrophorus sp.)
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Minimum Time Since Death

• The minimum time since death is determined
  largely by estimating the age of the maggots at
  the time the corpse is discovered.
• The fundamental assumption is that the person has
  not been dead longer than it took for the flies
  to arrive, lay eggs and maggots hatch and
  develop. Therefore, the oldest maggot determines
  the minimum time since death.

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Larva

• Larva hatch from the eggs and increase in size by
  growth steps called instars. Eventually the
  larva migrate from the corpse and develop into an
  inactive pupal stage. During this time, the
  adult insect develops internally.

Two larval instars.
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The Pupa and Adult Fly

• Once the maggot have finished feeding, they will
  pupate. During this process the maggot creates a
  hard brown shell around itself.
• Inside of the shell, the maggot turns into an
  adult fly. When the fly emerges the shell is left
  behind and becomes another clue.

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The Cycle of a Blowfly shows the time frame that
is used to determine the minimum time since death.
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Factors that affect maggot growth

• Factors such as weather, temperature, heat
  generated from the maggot mass, clothing and
  wounds will affect the growth of the maggots.
• Colder temperatures slow the growth of the
  maggots.
• If drugs are present in the body at the time of
  death, these toxins will also affect the rate of
  development.

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Pig Decomposition

• Pig decomposition is almost identical to human
  decomposition. Therefore, pigs are used in
  forensic entomological studies in order to better
  understand what happens when a human decomposes.

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Stages of A Pig Decomposition

• Complete metamorphosis
• involves development
• from egg to larva to
• pupa to adult. The pig
• ear in the diagram to the
• right shows a layer of
• what looks like a white
• crust. These are the fly
• eggs.

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Pig Decomposition
One day old dead pig showing signs of skin
changes and bloating. (Picture taken on
June 20th, 2002)
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Pig Decomposition
Advanced stages are seen on this one week old
dead pig. As the larva develop they migrate from
the body and develop into pupa.
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Collection Procedures

• In order to study the maggots, pupa and flies,
  they must be collected. Collections may be done
  in three differnet ways
• Aerial
• Hand
• Live Sampling

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Aerial Collection

• Use a net and sweep it back and forth over the
  decomposing body. Place them in a large jar with
  ethyl acetate. After a few seconds, use a funnel
  to move dead flies into a vial of 75 ethyl
  alcohol with a label of the date, time, case ,
  location, sample type and collector.

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Hand Collection

• Collect a variety of maggots with forceps. Place
  them in boiling water to stretch them out and fix
  them. Then place the maggots into a vial of
  alcohol with a label containing the date, time,
  case , location and collector.

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Live SamplingMaggot Motels

• Obtain a styrofoam container with a lid. Use sand
  or vermiculite for the bottom substrate. Place
  aluminum foil with beef or pork liver for food on
  top of the substrate. Collect 10 to 15 live
  maggots of varying sizes and drop them onto the
  foil. (You may also harvest and develop eggs in
  the motel.) Close the foil around them and
  allow to develop into pupae and then into adults.
  THEY MUST BE ADULTS IN ORDER TO IDENTIFY THE
  SPECIES.

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More Maggot Information

• Maggots collected from a dead body can be ground
  in a blender and tested for any toxins present in
  the body at the time of death. When the maggots
  feed on the dead tissue, they ingest these
  toxins.

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Maggot Therapy

• The medical field uses maggots to eat dead and
  decaying flesh on wounds. This allows the wound
  to heal sooner, but many people still find this
  disturbing!