Transcript Forensic Entomology

Forensic Entomology
Maggots and Time of Death
Estimation
Entomology is the
Study of Insects
Images from:
www.afpmb.org/military_entomology/usar
myento/files/ArmyEntomology.ppt
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”
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)
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
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.
Forensic Entomology is Applied Biology
• If it weren’t 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
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.
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 corpse’s
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
Image: http://www.nlm.nih.gov/visibleproofs
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
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
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
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 Fly’s 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.
Five Stages of Decomposition Fueled by Insect
Activity.
•
•
•
•
•
Fresh
Bloat
Decay
Post-decay
Dry (skeletal)
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.
Bloat
• Swells due to
gases produced
by bacteria
• Temperature rise
of the corpse
• Flies still present
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 it’s original mass.
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.
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 other 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.
Two Different Maggot Generations
• These are distinguishable by
the length and obvious size
difference.
• The photograph was taken
at a time consistent with
the influx at 132 hours.
The End