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Slide1
Entomology is the Study of Insects
Images from:
www.afpmb.org/military_
entomology
/usarmyento/files/Army
Entomology
.ppt Slide2
/
Forensic Entomology
Insects as Evidence
Warning: Some material in this presentation and related videos may be too graphic for some people. Slide3
What do they do?
Forensic
entomologists apply their knowledge of entomology to provide information for criminal investigations.
A forensic entomologist’s job may include:
Identification of insects at various stages of their
life cycle, such as eggs, larva, and adults.
Collection and preservation of insects as
evidence.
Determining an estimate for the postmortem interval or PMI
(the time between death and the discovery of the body) using factors such as insect evidence, weather conditions, location and condition of the body, etc.
Testifying
in court to explain insect-related evidence found at a crime scene.
Did you know? Maggots can be used to test a corpse for the presence of poisons or drugs. Some drugs can speed up or slow down the insect’s development. Slide4
Insects as Evidence
Forensic entomologists use their knowledge of insects and their life cycles and
behaviors
to give them clues about a crime.
Most insects used in investigations are in two major orders: 1 – Flies
(Diptera
) and 2 – Beetles
(Coleoptera
)
Blow Fly
Carrion Beetle
Images: Top Right - http://www.insectinvestigations.com/aboutfe.htm, Chart - http://www.clt.uwa.edu.au/__data/page/112507/fse07_forensic_entomology.pdf
Species
succession
may also provide clues for investigators
.
Some
species may to feed on a
fresh
corpse, while another species may prefer to feed on one that has been dead for two weeks.
Investigators
will also find other insect species that
prey
on the insects feeding on the corpse. Slide5
Examples of Diptera (Flies)
Informational Source: http://naturalsciences.org/files/documents/csi_tg_overview.doc
Images: Top Left - http://www.scienceinschool.org/repository/images/issue2forensic3_large.jpg, Middle-Left: http://forensicfact.files.wordpress.com/2008/04/blowfly053.jpg,
Top Right - http://users.usachoice.net/~swb/forensics/P1.jpg, Bottom - http://www.deathonline.net/decomposition/corpse_fauna/flies/index.htm
Flesh Fly
(Sarcophagidae)
S
triped thorax
Blow & Greenbottle Flies
(Calliphoridae)
Metallic thorax and abdomen
House Fly
(Muscidae)
Cheese Skipper
(Piophilidae)
Early Stage Decomposition
Late Stage Decomposition
Life Cycle of a Calliphoridae FlySlide6
Examples of Coleoptera (Beetles)
Informational Source: http://naturalsciences.org/files/documents/csi_tg_overview.doc
Images: http://www.cals.ncsu.edu/course/ent425/library/spotid/coleoptera/coleoptera.html & http://www.forensicflies.com/beetles.htm
Carrion Beetles
(Silphidae)
Adults & larvae feed on fly larvae
Early to Late Stage Decomposition
Late Stage Decomposition
Rove Beetles
(
Staphylinidae
)
Predator of fly eggs
Early Stage Decomposition
Hide Beetles
(
Scarabidae
)
Usually the last to arrive
Clown Beetles
(
Histeridae
)
Predator of fly eggs
Ham & Checkered Beetles
(
Cleridae
)
Predator of flies & beetles;
also feed on dead tissue
Skin Beetles
(
Dermestidae
)
Feed on dried skin & tissuesSlide7
Weather
data is also an important tool in analyzing insect evidence from a corpse.
Investigators
will make note of the temperature of the
air, ground surface, the interface area between the body and the ground, and the
soil under the body as well as the temperature inside any
maggot masses.
They
will also collect weather data related to daily temperature
(highs/lows),
and
precipitation
(humidity), and wind speeds
for a period of time before the body was discovered to the time the insect evidence was collected. Slide8
Other factors that might affect their PMI estimates:
Was the body
enclosed
in an area or wrapped
in a material that would have prevented flies from finding the corpse and laying eggs? a. Was the body (wrapped in a material, in a closed room, exposed to outside conditions, etc.)?
Were
other
insect
species present that may have affected the development of the collected species?
a. Not all fly species are found everywhere, and this can provide important information also. For example, the skipper fly,
Piophila
nigriceps
(pie-oh-FEEL-ah NYE-
greh
-
cehps
),
is found only in
urban
settings. House flies, blow flies, and flesh flies can be found in both urban and
rural
settings.
Were there
drugs
or other
poisons in or on the body that might have affected the larvae’s development? a. A drug like cocaine speeds up development in some larvae (so subtract days), while some poisons, such as arsenic , slow down development. Oleadrin is a glycoside and a powerful heart stimulant that speeds up development in Calliphora
vomitoria
(blowfly)
(so subtract 2-3 days).
Add this to your notes. Slide9
Did you know…
The “Body Farm” in Knoxville, Tennessee is a university research facility to investigate human decomposition under various conditions in order to understand the factors which affect its rate.
Click the image to view a video about the Body Farm!Slide10
Image: http://www.umext.maine.edu/images/FlyLife.jpg
Information: http://www.kathyreichs.com/entomology.htm and http://www.forensicentomologist.org/
Blow Fly Metamorphosis
1st – Adult flies lay
eggs
on the carcass especially at wound areas or around the openings in the body such as the nose, eyes, ears, anus, etc.
2nd – Eggs hatch into
larva
(maggots) in
12-24
hours.
3rd– Larvae continue to grow and
molt
(shed their exoskeletons) as they pass through the various
instar
stages.
1st
Instar
- 5 mm long after
1.8 days
2nd
Instar
- 10 mm long after
2.5 days
3rd
Instar
– 14-16 mm long after
4-5 days
4th – The larvae (17 mm) develop into pupa after burrowing in surrounding soil.
5th –
Adult
flies emerge from pupa cases after
6-8
days.
Blow flies are attracted to dead bodies and often arrive within
minutes
of the death of an animal. They have a
complete
life cycle that consists of egg, larva, pupa, and adult stages.
It takes approximately 14-16 days from egg to adult depending on the temperatures and humidity levels at the location of the body.
Adult
Eggs
Pupa
3
rd
Instar Larva
2
nd
Instar Larva
1
st
Instar LarvaSlide11
Image: http://www.nlm.nih.gov/visibleproofs Slide12
Flies, beetles, and many other insects have complete metamorphosis, which consists of four stages –
egg, larva
, pupa
, and adult.
After the adults mate, the females lay eggs onto corpses - usually near natural body openings or
wounds
.
http://www.cmnh.org/site/Img/ResearchandCollections/InvertZoo/124_blowflylifecycleRW.jpg
Metamorphosis
Feeding activity is usually seen in the
head
region first (mouth, nostrils, eyes, ears), followed by the excretory and reproductive openings. The
trunk
of the body is invaded much later in the process.
The length of the life cycle varies between different fly species and is dependent on
temperature
.Slide13
The maggot has a pointy end (mouth parts) and a blunt end.
a. The posterior segment of the blunt end contains
spiracles that are used for breathing
b. The pointy end is the anterior and has the mouthparts.
.
Diagram courtesy of Dr Ian Dadour,
Centre for Forensic Science, UWA
The MaggotSlide14
Figure 3: A diagram showing a cross-section of the posterior segment of a maggot.
A pair of spiracles is shown, each with 3 slits indicating a third stage maggot.
Diagram courtesy of Dr Ian
Dadour
, Centre for Forensic Science, UWA
The Posterior End of a MaggotSlide15
Phormia regina
Spiracles are incomplete
Third-instar larvae
Slide16
Phaenicia species
Spiracles are complete
Third-instar larvaeSlide17
Maggots commonly found on cadaversSlide18
Unemerged PupaSlide19
Emerging Adult from PupaSlide20
Adult BlowflySlide21
Adult BlowflySlide22
Things to Remember …
The progression of insect life follows a
pattern, and the developmental rates of flies are relatively predictable.
The rate of insect development is influenced by temperature because insects are
ectothermic
(“cold blooded”), which means their body temperatures are largely dictated by the
outside temperature. Only when the outside temperature warms an insect’s internal body temperature to its critical level can the insect become
active (and eat and grow).
As discussed previously:
The postmortem interval—the time between death and discovery of the corpse – can be estimated using insect evidence and temperature data along with other factors, such as the presence of drugs in a corpse and conditions related to the corpse itself (wrapped in a material, in a closed room, exposed to outside conditions, etc
.).
Any drugs present in the corpse at the time of death can affect the rate of maggot development, as they ingest the drug along with the tissue. A drug like cocaine speeds up development, while some poisons, such as arsenic and glycosides, slow it down.
Not all fly species are found everywhere, and this can provide important information also. For example, the skipper fly,
Piophila
nigriceps
(pie-oh-FEEL-ah NYE-
greh
-
cehps
),
is found only in urban settings. House flies, blow flies, and flesh flies can be found in both urban and rural settings.Slide23
Stages of Decay and decompositionSlide24
1.
Fresh Stage
Begins at the moment of death and lasts until the body becomes bloated.
Blow
flies and
flesh flies are among the first to find the body.
Predatory wasps and beetles may arrive later to feed on the maggots (but not the corpse). Slide25
Bloat
Stage
Begins when the body becomes inflated due to the production of
gases
from bacteria that begin to putrefy the body or cause it to decompose.
House flies now join the other flies and their maggots form feeding masses that help to liquefy the tissues of the body.
Slide26
Decay Stage
Begins when the skin breaks and the gases escape.
Maggot masses are large and very active as they grow older and larger.
This is the stage of decomposition that
smells
bad.
At the end of this stage, the maggots leave the corpse in search of a place to pupate in the soil. Slide27
Post-Decay Stage
Most of the
flesh
is gone from the corpse, with only cartilage, bone, and skin remaining.
This stage is devoid of flies. Some beetles continue to feed on the highly desiccated or dried remains.Slide28
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 reduviid insects such as the (assassin bug) etc.
The corpse is reduced to at least ten percent of the original mass.
In the last stage (Skeletal Stage), only bone and hair remain. Slide29
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.Slide30
The EndSlide31
T. Trimpe 2009 http://sciencespot.net/
Crime Solving Insects
Presentation developed for use with the Crime Solving Insects activity available at http://ipm.ncsu.edu/4-H/CSIfinal.pdf.
Image: http://www.animals-in-distress.net/files/photos/coriander2.jpg
What happened to Porky?Slide32
Case Studies
For each case:
1 – Review the police report and weather report.
2 – Examine & document the collected evidence.
Measure the length of the maggots & pupae. Record your data in the chart. Consult the Species Key and the tables on your lab page to determine the various fly species that were found on the corpse and their ages.
3 – Use the information from the reports and your examination to answer the questions. Slide33
Case #1: Oh, Deer!
Police Report:
The body of a female deer was found behind a fence along a busy two-lane road on the edge of the city limits of Charlotte. Animal Control was called and reported no apparent wounds on the body. It was not hunting season.
Weather Report:
Daytime temperatures have been fairly consistent for the past three weeks, ranging from 70 to 74º F.
Questions:
1. Approximately how long has this animal been dead?
2. Why are maggots of different ages found in the body?
3. Other than temperature, what abiotic
(external to the corpse) conditions would you want to obtain from the weather station to help you to be more confident of your time of death estimation?
Species & Stage
Size
(mm)
AgeSlide34
Case #2: Canine Caper
Police Report:
The body of a large pit bull terrier was found inside a walk-in basement at a home in Cary. Maggots were found concentrated in the head and region behind the shoulder. The windows were closed, although the open curtains allowed sunlight to enter, and the air conditioner was set at 72º F.
Weather Report:
Daytime temperatures have been variable over the past three weeks, ranging from 75 to 94º F. Skies have been sunny.
Questions:
1. Approximately how long has this animal been dead?
2. What effect, if any, do the outside temperatures have on your estimation of time of death in this case?
3. How does the fact that the windows were closed relate to the populations of flies you observed in and around the corpse?
4. Do you suspect foul play? Explain.
Species & Stage
Size
(mm)
AgeSlide35
Case #3: Dandy’s Death
Police Report:
The body of a young male horse was found in a pasture in a small town near Wilmington. The autopsy from the vet school reveals that the cardiac glycoside, oleandrin (a powerful heart stimulant), was present in the body. Oleandrin is found in the oleander plant. Oleander is a common ornamental shrub in this area, but none grows within 200 feet of the pasture.
Weather Report: Daytime temperatures have been unusually warm over the past three weeks, ranging from 84 to 86º F.
Questions:
1. Approximately how long has this animal been dead?
2. What effect, if any, does oleandrin have on your estimation of time of death?
3. What effect, if any, does temperature have on your estimation of time of death in this case?
4. Do you suspect foul play? Explain.
Species & Stage
Size
(mm)
AgeSlide36
Case #4: Porky’s Peril
Police Report:
The body of a large pot-bellied pig was found in a dense stand of evergreen trees far from any urban area in Buncombe County. Hairs around the pig’s neck were worn away in a band pattern.
Weather Report:
Daytime temperatures have been average over the past three weeks, ranging from 70 to 73º F. Temperatures in the woods would be approximately 5 degrees cooler due to the lack of sun in the shady environment.
Questions:
1. Approximately how long has this animal been dead?
2. What effect, if any, does temperature have on your estimation of time of death in this case?
3. Do you suspect foul play? Explain.
Species & Stage
Size
(mm)
AgeSlide37
chartSlide38
Crime Solving Insects Case Cards
Crime Solving Insects ScenariosCrime Solving InsectsSlide39
VIP Forensic Filesinsects and distinguishing features VIP filesSlide40
Forensic entomology card
Forensic entomology notesSlide41Slide42
Click the image above or click here to visit the website at
http://www.pbs.org/wnet/nature/episodes/crime-scene-creatures/interactive-determine-the-time-of-death/4390/
Let’s give it a try …