Transcript 4_Entymology - bloodhounds Incorporated

Forensic Entomology
The Role of Insects in Medico-legal Death Investigation
Forensic Entomology
Forensic Entomology
Forensic Entomology is the use of insect
knowledge in the investigation of crimes.
Forensic Entomology is not only a useful
tool to decide how long human remains
have been undetected, but forensic
entomology can also be used to find out
whether the corpse has been moved after
death, the cause of death and also solves
cases of contraband trafficking (Catts,
1995).
Forensic entomology can be
divided into three categories
Urban
Store-product
Medicolegal
Urban forensic entomology
deals with insects that
affect man and his
immediate environment
May deal with pest infestations
where there might be litigation,
for example, landlord and
tenants.
Stored-product forensic
entomology concentrates
on commonly found insects
in contaminated foods.
Legal issues on insect
infesting stored products
Medicolegal, which we
primarily focus on, deals with
the criminal component of the
legal system and with insects
that typically infest human
remains or corpses.
Use of insect development
and insect colonization to
solve crime(s)
Medico-legal Entomology
Helps determine postmortem interval
Movement of body???
Determine scene of death
Proves or disproves suspect, witness or
corroborating statements regarding death
 http://www.smithsonianchannel.com/site/sn/show.do?episode
=141561
 http://www.smithsonianchannel.com/site/sn/show.do?episode
=141561 - measuring-time-with-maggots
Some History
1200s – Sung Tz’u, a Chinese “death
investigator” uses the behavior of flies to
solve a murder. Everyone in the small town
where the murder took place is gathered
together with their sickles (blades used for
cutting grass). Though no obvious blood
stains appear on the tools, Tz’u releases
flies into the area which, drawn to the scent
of blood, buzz around the murder weapon.
The guilty person confesses.
1668- Francesco Redi disproves the
theory of spontaneous generation of
maggots in rotten meat. The prevailing
thought of the day was that maggots
appear from nowhere in the spoiled food,
as if by magic. His experiment showed
that the life cycle of the maggot is
associated with the rate of decay,
allowing scientists to better estimate a
deceased person’s time of death.
1750s – 1780s – Carolus Linnaeus
published a standardized system of
biological classification. Scientists use this
system to determine the location of a
murder, as fly species live in certain
habitats.
1855 – Dr. Berger d’Arbois, France’s
premier coroner of the day, proves the
innocence of residents of a home in
which a body is found. By studying fly
larvae and mites in the body he
determines that they were laid before the
body was sealed inside the home of the
accused well before the current residents
moved in.
1894 – Dr. Jean-Pere Megnin publishes.
The Fauna of Corpses, describing eight
stages of bodily decomposition. Included
in these are the types of insects each
stage attracts. This further aids scientists
in determining a victims time of death
and if the body has been moved.
1935 – Dr. Alexander Mearns of Glasgow
University uses the development of
maggot larvae in a body to determine the
victim’s time of death. This, in conjunction
with witness testimony and other
evidence, allows a suspect to be
convicted in court.
1986 – The first textbook devoted to
forensic entomology, A Manual of
Forensic Entomology, is published. This
makes information on this branch of
forensics readily available, allowing
standardized training for aspiring
scientists.
Maggot Mass
Medicolegal Entomology
Typically focuses on violent crimes
Determination of time of death
Determination of crime scene
A Forensic Entomologist:
Identifies the immature insects
Determines the size and development
of the insects
Calculates the growth of the insects
and the stages of the life cycle
Compares the growth against weather
conditions to estimate time of
ovipositions (egg laying)
Corpse as Insect Food Source
Bodily decomposition attracts flies
 Flies and related insects have highly sensitive
olfactory receptor sites on top of head.
 Attracted to protein-rich environment which corpse
provides
 Insect activity on the corpse within minutes of
death
 Deposits eggs in natural or unnatural openings,
a.k.a., orifices or exposed wounds – eyes, ears,
anus, etc.
 Deposits eggs in orifices during daylight
Forensic Entomology
 After the initial decay, and
the body begins to smell,
different types of insects
are attracted to the dead
body.
 The insects that usually
arrives first are the
Necrophages, which
includes flies (Diptera)
such as the blowfly
(Calliphoridae) and the
flesh flies (Sarcophagidae).
 Blowflies and flesh flies are
very important to the
forensic entomologist
Calliphorid Flies
Adult flies can be
identified by the
iridescent blue, green
colors
Sarcophagid Flies
These flies are grayish
with longitudinal dark
stripes on the dorsum
Omnivores
 Omnivores, which include
wasps, beetles and ants
feed on the corpse along
with the maggots left by
the flies.
 Omnivores may slow the
rate of decomposition by
decreasing the
population of
necrophages
Parasites and Predators
 Parasites and Predators –
beetles and wasps eat
immature flies
 Others – spiders, mites,
pill bugs and others use
the corpse as a source of
habitat
Forensic Entomology
 Eggs are laid around
the natural orifices
such as the nose,
eyes, ears, anus,
penis and vagina.
 If the body has
wounds the eggs are
also laid in such.
 Flesh flies do not lay
eggs, but deposits
larvae instead.
Insect Evidence
Some species feed on fresh corpse, while other
species prefer to feed on a corpse that has been
dead for two weeks.
Investigators also find other insect species
that prey on the insects feeding on the
corpse.
Cleoptera
Forensic Entomology
The usual sites of oviposition on dead
humans are natural openings.
Blowflies will most often lay their eggs in
the facial region, and more seldom in the
genitoanal region.
 If there is a sexual assault prior to death, leading to
bleeding in the genitoanal region, blowflies will be
more likely to oviposit in these regions.
 If there’s blowfly activity in the genitoanal region, a
sexual crime is suggested.
Forensic Entomology
The sites of blowfly infestation on the
corpse may be important in
determining the cause of death
 For example: if there has been trauma or
mutilation of the body prior to death, this
may lead to heavy infestation of other body
parts than the usual sites when the victim
is not mutilated.
 Under a knife attack, it is usual to guard
oneself with arms in front of thorax and
head. This may lead to injury on the lower
part of the arm. After death, blowfly may
oviposit in these wounds.
Blow Fly Life Cycle:
Eggs
 Laid on a host
which is typically
dead.
 May be laid within
minutes of death.
 Eggs typically
hatch within 24hours of
depositing
Blow Flies
 Insects are cold-blooded so their
development is temperature dependent
 As temperature increases, they develop
more rapidly
 As temperature decreases, they develop
more slowly
Fly Eggs
Fly eggs look
like
parmesan
cheese and
accumulate
in moist
areas
Fly Larva
Eggs hatch within 24 hours after being
laid
Fly larva are also known as maggots
1st Instar Stage – 1.8 days (5 mm long)
The larva will eat until it gets so big it
needs to shed its skin
First Instar
Initially feeds on
fluid exuded from
the body
Migrates into
body
Hatching to first
molt takes 1.8
days
Fly Larva
2nd Instar Stage – 2.5 days (10 mm
long)
For another 24 hours these maggots
will grow until they shed their skin
again
Third Instar
Still moves in
mass
Greatly increases
in size
Second molt to
pre-pupa takes
2.5 days
Fly Larva
3rd Instar Stage – 4 –5 days (17 mm
long)
Feeding 3rd instar – maggots are eating
Migrating 3rd instar – maggots stop
eating and start moving to the soil
under the body
Maggots are in the 3rd instar for about
100 hours
Pupa
Once the maggots are deep within the soil they
will go through the pupation in order to become an
adult fly.
 10 –14 days after oviposition (lay eggs)
 Pupa (made of chitin; a hardened protein based
substance to protect developing insect that is encased)
 Many investigators overlook the dried, hardened outer
skin of the larva that is left in the environment when
the fly emerges.
PUPA
Fly pupae are often discovered away from the
body since maggots migrate. These pupae
should be recovered at the death scene if time
of death is questionable.
Blow Flies
Analysis of the oldest insect stage on
the body, together with knowledge of
the meteorological conditions at the
scene, can be used to determine how
long insects have been feeding on the
body, and hence, how long the victim
has been dead
Almost complete
skeletonization of
the head by
maggots
Young maggots resemble fly eggs but
are mobile.
Fly pupa and other
insects present on
decedent.
Post-morten ant and roach
Activity leaves a typical
grouped pattern that
looks like an abrasion
Post Mortem Interval
PMI – time interval from actual death to
discovery of the body.
Cadavers decompose in four stages:
 Fresh
 Bloated
 Decay
 Dry
Certain insects are attracted to the corpse in
each of the four stages of decomposition.
 Succession = the order in which insects are
attracted to the decomposing body
 Succession pattern is useful to determine PMI
Post Mortem Interval
Blowflies are attracted to a fresh corpse
in order to lay their eggs
Carrion flies are attracted to the bloated
corpse
There is a succession database that can
be used to estimate PMI
Factors Used to Determine Time Since Death
4 factors must be taken into account
 Oldest stage of blow fly associated with the
body
 Look at old pupal cases
 Species of insects
 Each species develop at different rates so each
species of insects at the scene need to be collected
 Temperature data
 Must be able to determine temperature of crime
scene for a period of time
 Developmental data
 Must know how fast or how slow the specific species
develop
Degree Hours
Degrees since death
The life cycle of the insect is measured
by degree-hours because temperature
effects the cycle
Calculating PMI from
Accumulated Degree Hours (ADH)
From
Egg
To
Temp Hours
1st Instar 70° F
ADH
Cumulative ADH
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
1610+1890+
1540
3rd Instar
Pupa
70 °
F
130
130 x 70= 1610+1890+
9100 ADH 1540+9100
Pupa
Adult Fly
70 °
F
143
143 x 70= 1610+1890+
10010 ADH 1540+9100
+10010
Calculating ADH from Climate Data
Using the Data
3928 ADH in these three days (952+1488+1488).
How many ADH of 70º are there in these 3 days?
3928/70=56.11 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.
Determining Whether the Body has been
Moved
Insects present on the deceased body
that are not prevalent to the crime
scene can indicate that the victim was
murdered elsewhere and was dumped
at another location
Linking Suspect to Scene
Sometimes, criminals carry entomological
evidence on them unknowingly
This evidence can place them at the crime
scene by examining the life cycles of the
insects
Drugs
Insects that feed on the body of
individuals that have been poisoned
can be examined to determine what
type of drug or toxin the person was
poisoned with
It is important to note that specific
drugs either speed up or slow down
larval development
Can influence entomologist’s final
report
Forensic Entomology
 Analysis of larvae can assist in the
identification of drugs used by decedent as
well as their DNA
• Triazolam
• Oxazepam
• Alimemazine
• Chloripriamine
• Phenobarbitol
• Malathion
• Mercury
• Amyltryptiline
• Nortriptyline
• Cocaine
• Phenycyclidine
• Heroin
Forensic Entomology
Many of these chemicals will also
influence the life-cycle of the maggot.
 Cocaine accelerates the development of
some sarcophagids.
 Malathion, an insecticide, is commonly
used in suicide, and is usually taken orally.
 Amitriptyline, an antidepressant, can
prolong the developmental time up to 77
hours, at least in one species of
Sarcophagidae.
Collection of Entomological
Evidence
Evidence should be collected by an
entomologist
If not available, a police death investigator
should collect the evidence
Different stages of larval growth should be
collected and bagged separately
Sample of soil should also be collected from
just outside the area marked by body fluids
Challenges to Forensic
Entomology
 3 challenges exist
 Temperature
 Temperature of crime scene and the temperature that the insects
have been exposed to us unknown
 Season
 Entomology is valuable only in spring, summer, and fall
 Exclusion of insects
 Insects are excluded based on condition of body
Forensic Entomology
Blow fly pupae were collected from
a body found.
The ambient temperature was
approximately 75°F and the
humidity was 20%.
Larva found on the body were
approximately 10mm long.
Estimate time since death.
Case Study (Decomposition)
On a hot August day (90°F), the body
of an elderly man was discovered in a
ditch next to a country road. He was
lying supine dressed in overalls, a
short-sleeved work shirt, and socks
without shoes. His abdomen and legs
were covered by a blanket. There was
marked maggot infestation of the head
and neck, partially obscuring a
posterior scalp defect, and a ligature
around his neck.
Case Study (Decomposition)
The skin of the upper chest,
neck, and head were markedly
darkened. The rest of the body
was not decomposed. There
was a slight greenish tinge to
the abdominal area. There was
no apparent blood on the
ground surrounding the victim.
Case Study (Decomposition)
The scalp defect was a four inch gaping
laceration with no underlying bone or brain
injury. The ligature was a small towel tightly
compressing the neck and knotted in the
back. There was no rigor mortis and livor
mortis was posterior. When the body was
turned the livor did not move with gravity.
Case Study (Decomposition)
Stomach contents revealed
fragments of sausage pieces, brown
liquid and white semi-solid food
particles. At least ten maggots were
saved in a container of alcohol. The
largest maggot was 4mm in length.
A diagnosis of ligature strangulation
was rendered and the death was
ruled a homicide.
Case Study (Decomposition)
When the wife came in to view his
body she made a spontaneous
statement, “I don’t understand, he
looks fatter than normal.”
Case Study (Decomposition)
The next day a deputy sheriff called
the pathologist to ask about the time
of death. The deputy was holding a
man in custody who had been seen
with the decedent two days before the
body was discovered. The suspect
claimed that he was out of town the
day before the man was found dead.
The suspect had a good motive for the
murder because of a soured business
deal with the victim.
Case Study (Decomposition)
Prior to making a formal arrest,
the officer needed to make sure
the postmortem interval was
consistent with two days. What
should the pathologist say about
the postmortem interval in this
case and why?