Transcript Time of Death

Determining the Time of Death (TOD)
Maggots and Murder
Forensic Entomology
Using the developmental stages of insects to determine TOD
Larvae
Pupae
Eggs
Adult
Adult
Forensic Entomology
The study of insects in relation to a criminal
investigation.
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
Determining the Time of Death (TOD)
Using Forensic Entomology
Stages of Decomposition
1. Initial Decay-Although body shortly after death
appears fresh from outside-bacteria in body’s
intestine before death begin to digest intestine itself.
• Autolysis-bacteria exit intestine and digest internal
organs. The body's own digestive enzymes spread
throughout body
• Enzymes inside cells-released when cell dies-break
down cell and connections with other cells
• Flies are immediately attracted to dead bodies
Without normal defense of living animal- blowflies
and house flies lay eggs around wounds and body
openings
• Eggs hatch and move into body within 24 hours. Life
cycle of a fly from egg to maggot to fly-2-3e weeks
Stages of Decomposition
2. Putrefaction-4-10 days after death
• Putrefaction-destruction of soft tissues by of microorganisms-results in catabolism of tissue into gases
and liquids
• First visible sign-formation of sulfhaemoglobin in
settled blood.
• Releasing fluids into body cavities-anaerobic
respiration - produce hydrogen sulphide, methane,
cadaverine, putrescine, butyric and propionic fatty
acids
• Distention of gut-Gas build up from multiplying
bacteria-internal pressure-inflates body and forces
fluids from cells and blood vessels into body cavity
• Rate of decay increases-blowflies, flesh flies, beetles
and mites
• Late-arriving insects-predators-feed on maggots and
flesh -Maggot masses
One day old dead pig showing signs of skin changes and bloating.
Stages of Decomposition
3. Black Putrefaction-11-20 days after death
• Bloated body collapses-creamy flesh-exposed parts are black in
color and very strong smell of decay.
• Body fluids drain from body and seep into soil
• Insects consume most of the flesh and body temperature
increases with activity.
• Bacterial decay important-bacteria consume body if insects are
excluded
• Several generations of maggots-migrate from body and bury in
soil to pupate
• Predatory maggots are much more abundant
• Pioneer flies cease to be attracted to corpse.
• Predatory beetles lay their eggs in the corpse and their larvae
then hatch out and feed on flesh
One week old pig-larva develop & migrate from body to pupate
Butyric Fermentation
• 20-50 days after death
• Dessication of corpse-remaining flesh is removed
and butyric acid released
• The surface of body in contact with ground becomes
covered with mold as body ferments.
• Beetle larva and adults feed on skin and ligaments.
• Predators and parasitic wasps and beetles
Dry Decay
• 50-365 days after death
• Body is dry and decays slowly-Eventually
leaving only skeleton
• Diagenesis-process that changes
skeleton’s proportions of organic
(collagen) and inorganic components
(hydroxyapatite, calcium, magnesium)
PMI--Postmortem Interval
PMI-amount of time b/w TOD and body’s discovery
Estimation of PMI- set minimal and maximal PMI
Minimal PMI -determined by estimating age of
developing immature insects collected when corpse is
discovered
Maximum PMI-determined from species of insects
present and weather conditions needed for the activity
of these species
Temperature
Ambient heat plays a role
during egg and early
larval development but
after that its effect
decreases rapidly.
Maggot masses generate
their own heat.
Taking temperature of the maggot mass
can find it as high as 125 degrees F.
Forensic Entomology
Using developmental stages of insects to determine
TOD
Larvae
Pupae
Eggs
Adult
Adult
Forensic Entomology
• The study of insects in relation to a criminal
investigation
• Insects arrive at decomposing body in a sequence and
complete their life cycle based on surrounding
temperature
• Forensic entomologist can predict the time of death
Metamorphosis
Complete metamorphosis
(holometabolous) development from egg to
larva to pupa to adult
The white crust in the
picture are the fly eggs.
Larva
Larva hatch from the eggs and
increase in size by growth steps
called instars.
Larva migrate from corpse and
develop into an inactive pupal
stage
During this time, the adult insect
develops internally.
Two larval instars.
The Blowfly
• Acts as both necrophages and as predator
• One of the most common species on dead
bodies
• Often arrive within 10 minutes
• Feed on blood and lays eggs in body cavities
• If food source is exhausted- will prey on other
species in same genus (Chrysomya)
• Maggots (fly larvae) are remarkable eating
machines
• Posterior spiracles
• Spiracles are used for breathing-posterior
spiracles-means that maggots can breath &
feed 24 hrs a day
First instar
Third Instar
Second instar
Pupal Stages of House Fly
Types of Insect Collections
Collection are done in three ways:
– Aerial
– Hand
– Live Sampling
Aerial Collection
• Use a net in figure 8 motion over
cadaver
• Collect flies and put them in ethyl
acetate
• After a few seconds-put flies into
75% ethyl alcohol-label date, time,
case #, location, sample type and
collector.
Live Sampling
“Maggot Motels”
• Collect 10 to 15 live maggots of varying sizes into a rearing
chamber
• Allow to develop into pupae and then into adults.
Hand Collection
• Collect maggots with forceps
• Put in boiling water to stretch
them out and fix them
• Put maggots into ethanol with a
label containing date, time, case
#, location and collector
First instar
Third Instar
Second instar
Maggots can consume 60 per cent of a corpse in less than a
week. Video footage: R. Major
Windows Media (77kb)
Quicktime (275kb)
Burying
Beetles
Hister Beetle
Forensic Flies