Forensic Science Unit 4

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Forensic Science Unit 4

• Forensic Biology Day One
• Entomology

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Get out your Time of death packet

• If you turned it in last class period it should
  be in your folder

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Forensic File 3

• Part 1 A body has been found in a field with an
  internal temperature of 83oF. Using 1.4oF lost
  every hour, what is the PMI (post mortem
  interval)? In other words, how long have they
  been dead?
• Part 2 What if the internal temperature of the
  body was 73oF? How long have they been dead?

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Your assignments

• Insect Webquest
• Body Bugs article questions
• Paper on TABLE 4

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What is Forensic 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

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What are the different life cycles of insects?

• Incomplete Metamorphosis
• 3 stages
• Egg
• Nymph has appearance of small adult increases
  size with each molt
• Adult

• Complete metamorphosis
• 4 stages
• Egg
• Larvae wormlike stage (caterpillar)
• Pupa inactive stage (chrysallis)
• adult

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Complete metamorphosis

• Holometabolous
• The pig ear in the diagram shows a layer of what
  looks like a white crust. These are the fly eggs

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Larva

• Larva hatch and grow in steps called instars
• Eventually the larva migrate from the corpse and
  develop into the pupal stage
• During this time, the adult insect develops
  internally

Two larval instars
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Four Main Types of Carrion Species

• Necrophagous--feed directly on the corpse
• Flies (Diptera)
• Beetles (Coleoptera)
• Predators
• Burying or Carrion beetles (family Silphidae)
• Rove beetles (family Staphylinidae)
• Hister beetles (family Histeridae)

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Four Types continued

• 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 Blow Fly
Black

• Acts as both necrophages and as a predator.
• One of the most common species on dead bodies
• Often arrive within 10 minutes
• Feed on any blood or fluids and then start laying
  eggs in and around the natural body cavities
• If the food source is exhausted, they will prey
  on other species in the same genus (Chrysomya)

Green
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Blow Fly continued

• Blowflies seek moist areas of the corpse to lay
  their eggs
• The nose, mouth, armpit, groin and open wounds
  are favored locations
• Eggs hatch into maggots within 24 hours
• Usually reach length of 1cm after 3 days
• During the next 6 to 10 days they feed, grow and
  repeatedly molt
• Become a pupae when their outer covering hardens
• Approximately 12 days later adult flies emerge