Transcript Forensic Entomology - Madison County School District

Forensic Entomology
Also Included: Maggot Therapy
and Taxidermy
Forensic Entomology Relies Strongly
on the Following Ecological Concepts
► Developmental
time is temperature
dependant at the microhabitat level.
► Ecological succession – A corpse will be
invaded by a series of different species or
insect groups over time. Each species or
group changes the microenvironment
through its activities which makes it
attractive to new waves of organisms and
so on.
The Most Common Application
Relates to Death Investigations
► Determining
PMI – postmortem interval
► Movement of the corpse
► Manner and cause of death
► Association of suspects with the death
scene
► Detection of toxins or drugs through
analysis of insect larvae
Estimates of PMI Using Insects May
Be Based On:
► Period
of time for a given species to reach a
particular stage of development
► Comparisons of assemblages of insect fauna
on corpse at time of examination
► A combination of both above
Most Important Environmental
Factors in Corpse Decay*
► Temperature
► Access
by insects
► Depth of Burial
►*
Based on study of decay rates of 150 human corpses
at U. of Tenn.
Ecological Roles of Insects in
Decomposition
► Necrophages
– species feeding on corpse tissue;
mostly true flies and beetles; age determination
(larval instar) important for PMI
► Omnivores – insects that feed both on the corpse
and associated fauna; ants, wasps and some
beetles; may alter rate of decomposition
► Parasites and Predators – many beetles, true flies
and wasps that attack immature flies
► Incidentals – use the corpse as a resource
extension; springtails, spiders, centipedes, some
mites
Five Stages of Human Decomposition Have
Been Recognized -1
► Fresh
Stage (Days 1-2) – From moment of
death to first sign of bloating; flesh flies,
blow flies, ants eating fly eggs and
predatory wasps;
Flesh Flies – 2 Species
Two Blowfly Species
Blowfly Larvae
House Flies on Dead Host
Five Stages … 2
► Bloated
stage (Days 2-6) – putrefaction
begins; gases produced by anaerobic
bacteria; considerable bloating; seepage of
fluids; adult and larval blowflies attracted in
large numbers to seepage; soil fauna moves
away due to wetness of earth; ants and
other species of flies prey on maggots
Five Stages … 3
► Decay
Stage (Days 5-11) – Abdominal wall
is broken and carcass deflates; adult flies
begin to leave but great masses of maggots
remain and feed; carcass will begin to dry
and beetles begin feeding on drier tissue;
flies start to pupate; predatory beetles such
as rove and hister beetles are attracted
Pig Carcass Infested With Blowfly
Maggots
Hister Beetles Prey on Blowfly Larvae
Rove Beetles – 2 Species
Five Stages … 4
► Postdecay
Stage (Days 10-25)
 in dry habitats - remains consist of dry skin,
cartilage and bones; site for dermestid beetles,
histerids, fly pupae, immature and adult rove
beetles
 in wet habitats – large quantities of wet, viscous
material (byproducts of decomposition) found in
soil under the remains; site for adult and
immature moth flies, rove beetles
Dermestid Beetles – Adult and
Larvae
Five Stages … 5
► Dry
Stage (Days 25+) – Mainly bone and
hair is all that remains; odor is primarily that
of soil and litter; some dermestids, fly
pupae, immature and adult rove beetles,
normal soil fauna consisting of mites, etc.
start to return; this stage could last for
several months to years
Carrion Beetles – 2 Species
Female Carrion Beetle and
Kangaroo Rat
Rat will be completely buried and eggs
laid upon it.
Barriers to Decomposition and
Irregular Decomposition
► Physical
– soil, water, caskets, antermortem
and postmotem injuries
► Chemical – embalming agent, insecticides,
lime, etc.
► Climatic – heat, cold, wind, rainfall
► Animals – bird, mice, rodents, canids, cats,
etc.
Maggot Therapy – Technically called Maggot
Debridement Therapy or MDT
Fly larvae are used to scavenge on
dead tissue associated with a wound.
Fly larvae excrement, termed allantoin
has a high ammonia content which
appears to serve as an antibiotic.
Wounds on the Battlefield in World
War II
It has been noted by war surgeons that wounds
incurred by troops in which fly larvae were
feeding had much less gangrene and healed
more quickly than wounds that were protected
from flies …
Phaenicia sericata – the green blow fly.
This species feeds only on necrotic
(decayed) tissue.
Interesting and True …
► Maggot
therapy is much more commonly
used in Great Britain and Europe than in the
U.S.
► There have been about 25,000 treatments
in Great Britain since 1995.
► Ronald Sherman, M.D. is the pioneer of
maggot therapy in the U.S. He is located at
U. of Calif., Irvine.
Maggots Feeding at Edge of an
Ulcerating Wound on Foot
Maggots Cleaning Up a Wound
Associated with an Amputation
Vertebrate Biology/Taxidermy –
Skull and Skelton Preparation
A Skull Cleaned by
Dermestid Beetles
Trays of Vertebrate Skulls in Dept. Of
Vertebrate Biology, Univ. of Michigan
A Great Horned Owl Skeleton
Dermestid Colony Housing
Larval and Adult Dermestids
Working on Jawbone
Bear’s Skull Being Cleaned
Dermestid Beetles Are Economic Pests and
Will Scavenge on Anything Organic of Both
Plant and Animal Origin
► Destroy woolen carpets, upholestry and
rugs
► Consume insects on pins in museum and
university collections
► Stored furs, leather and skins
► Meat, cheese and stored products
► Materials made of silk
Dermestids are Beneficial in Terms of
► Their
use in vertebrate skull/skeleton
collections
► Their forensic use as we have seen