Maggots and Time of Death Estimation

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Forensic Entomology

• Maggots and Time of Death Estimation

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Entomology is the Study of Insects Images from
www.afpmb.org/military_entomology/usarmyento/files
/ArmyEntomology.ppt
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Insect Biology

• Insects are the most diverse and abundant forms
  of life on earth.
• There are over a million described species- more
  than 2/3 of all known organisms
• There is more total biomass of insects than of
  humans. of humans.
• Insects undergo either incomplete or complete
  metamorphosis (Egg to larva to pupa to insect)
• Larva have a soft tubular body and look like
  worms. Fly species larvae are maggots

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What is Forensic Entomology?

• Forensic Entomology is the use of the insects and
  other arthropods that feed on decaying remains to
  aid legal investigations. 
• Medicolegal (criminal)
• Urban (criminal and civil)
• legal proceedings involving insects and related
  animals that affect manmade structures and other
  aspects of the human environment
• Stored product pests (civil) 

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Medicolegal Forensic Entomology

• Often focuses on violent crimes
• Determination of the time (postmortem interval or
  PMI) or site of human death based on
  identification of arthropods collected from or
  near corpses.
• Cases involving possible sudden death
• Traffic accidents with no immediately obvious
  cause
• Possible criminal misuse of insects

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Postmortem interval (PMI)

• Forensic Entomology is used to determine time
  since death (the time between death and corpse
  discovery)
• This is called postmortem interval or PMI).
• Other uses include
• movement of the corpse
• manner and cause of death
• association of suspects with the death scene
• detection of toxins, drugs, or even the DNA of
  the victim through analysis of insect larvae.

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Forensic Entomology is Applied Biology

• If it werent for decomposition of all living
  things, our world would fill up with dead bodies.
  
• When an animal dies, female insects will be
  attracted to the body. They enter exposed
  orifices or wounds and lay eggs or larvae.
• A forensic entomologist
• identifies the immature insects
• determines the size and development of the
  insects
• calculates the growth of the insects and passage
  through stages of the life cycle in laboratory
• compares the growth against weather conditions to
  estimate time of oviposition

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Succession of Insects on the Corpse

• Estimates of postmortem intervals based on
  insects present on the remains are based on
• The time required for a given species to reach a
  particular stage of development.
• Comparisons of all insect species present on the
  remains at the time of examination.
• Ecological succession occurs as an unexploited
  habitat (like a corpse) is invaded by a series of
  different organisms.
• The first invasion is by insect species which
  will alter the habitat in some form by their
  activities. These changes make the habitat
  attractive to a second wave of organisms which,
  in turn, alter the habitat for use by yet another
  organisms.

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Ecology of Decomposition

• Necrophages - the first species feeding on corpse
  tissue. Includes rue flies (Diptera) and beetles
  (Coleoptera).
• Omnivores - species such as ants, wasps, and some
  beetles that feed on both the corpse and
  associated maggots. Large populations of
  ominvores may slow the rate of corpses
  decomposition by reducing populations of
  necrophagous species.
• Parasites and Predators - beetles, true flies and
  wasps that parasitize immature flies.
• Incidentals pill bugs, spiders, mites,
  centipedes that use the corpse as an extension of
  their normal habitat

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Image http//www.nlm.nih.gov/visibleproofs
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Decay Rates Are Variable

• Studies of decay rates of 150 human corpses at in
  the Anthropological Facility in Tennessee (The
  Body Farm)
• Most important environment factors in corpse
  decay
• Temperature
• Access by insects
• Depth of burial
• Other Factors
• Chemical-- embalming agent, insecticides, lime,
  etc.
• Animals disrupting the corpse

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Time of Death can be broadly estimated up to
about 36 hours
Temperature Stiffness Time of death
Warm Not stiff Dead less

than three hours
Warm Stiff Dead between 3

to 8 hours
Cold Stiff Dead between 8

to 36 hours
Cold Not stiff Dead in more

than 36 hours
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Differentiate between PMI and Time of Death

• These may not always equate.
• Post mortem interval is restricted to the time
  that the corpse or body has been exposed to an
  environment which would allow insect activity to
  begin.
• Closed windows
• Body in box or bag
• Cold temperatures
• Deeper burial

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Insect species arrive at a corpse in waves like
clockwork

• Calculate the heat/thermal energy (accumulated
  degree hour) required for each stage of the Green
  Bottle Flys life cycle.
• Possibly the greatest potential source of error
  in using arthropod successional patterns lies in
  the collection of speciments.
• Must only be done correctly to accurately sample
  the insects.

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Image http//www.nlm.nih.gov/visibleproofs
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Calculating PMI from Accumulated Degree Hours
(ADH)
From To Temp Hours ADH Cumulative ADH
Egg 1st Instar 70 F 23 23 x 70 1610 ADH 1610
1st Instar 2nd Instar 70 F 27 27 x 70 1890 ADH 1610 1890
2nd Instar 3rd Instar 70 F 22 22 x 70 1540 ADH 16101890 1540
3rd Instar Pupa 70 F 130 130 x 70 9100 ADH 16101890 15409100
Pupa Adult Fly 70 F 143 143 x 70 10010 ADH 16101890 15409100 10010
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Calculating ADH from Climate Data
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Using the Data

• 3928 ADH in these three days (95214881488).
• How many ADH of 70º are there in these 3 days?
• 3928/7056.11 hours
• 72 hours at 70º would have the insects passing to
  the 3rd instar. But 72 hours at colder
  temperatures and insects will only be at 2nd
  instar stage.

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Five Stages of Decomposition Fueled by Insect
Activity.

• Fresh
• Bloat
• Decay
• Post-decay
• Dry (skeletal)

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Fresh

• Begins at death
• Flies begin to arrive
• Temperature falls to that of the ambient
  temperature.
• Autolysis, the degradation of complex protein
  and carbohydrate molecules, occurs.

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Bloat

• Swells due to gases produced by bacteria
• Temperature rise of the corpse
• Flies still present

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Decay

• Gases subside, decomposition fluids seep from
  body.
• Bacteria and maggots break through the skin.
• Large maggot masses and extreme amounts of fluid.
• Unpleasant odor
• Larvae beginning to pupate.
• Corpse reduced to about 20 of its original mass.

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Post-Decay

• Carcass reduced to hair, skin, and bones.
• Fly population reduced and replaced by other
  arthropods.
• Hide beetles are dominant in dry environments.
• Mite and predatory beetle populations increase.

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Dry (Skeletal)

• Does not always occur especially if corpse is in
  a wet region. Maggots will stay longer and hide
  beetles will not appear.
• In wet environments the hide beetles are replaced
  with nabid and reduviid insects.
• The corpse is reduced to at least ten percent of
  the original mass.
• In the last stage (Skeletal Stage), only bone and
  hair remain.

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Accumulated Degree Hours

• ADH may be calculated using temperature and
  hours.
• This works because there is direct correlation
  between temperature and maggot development.
• These calculations were somewhat approximate but
  relatively accurate.

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Review Questions 1-9

• What is Forensic Entomology?
• Explain 5 applications/uses of insects in
  forensic science.
• Describe the stages of death Algor Mortis Livor
  Mortis Rigor Mortis.
• Describe the stages of decompositions.
• What are the most important environmental factors
  in corpse decay?
• Identify the name and origin of chemical released
  during each stage of decomposition.
• Why is it important to know what chemicals are
  produced as the body proceeds through
  decomposition?
• What are the 2 insect orders most commonly found
  on a decaying corpse.
• Describe the life cycle of the Insects found on a
  decaying corpse. How does this life cycle help
  explain time of death.

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Review Questions 10-15

• What is postmortem interval (PMI)?
• Time of death can be estimated up to about 36
  hours using temperature and stiffness. Explain
  how temperature and stiffness is used to estimate
  time of death
• Explain the difference between (PMI) and time of
  death.
• What is Accumulated Degree Days (ADD) and
  Accumulated Degree Hour (ADH).
• How is the (PMI) used to calculate (ADH or ADD)?
  Provide an example?
• Explain the proper techniques, equipment and
  procedures required for collecting insects for
  use in forensic investigations.