Transcript Chapter 12 Forensic Entomology

Chapter 12
Forensic Entomology
Case study – Bugs Don’t Lie
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When did the children go missing?
When were the bodies found?
List 5 reasons for suspecting the stepfather.
Summarize the entomological evidence and explain how
this lead to estimating the time of death.
Introduction
O Forensic entomology – use of insects in
legal investigations
O Phylum Arthropoda – insects, spiders,
scorpions, crayfish, and millipedes
- invertebrates
- externally segmented bodies
- exoskeleton made of chitin
Historical Development
O Fig. 12-3 p. 344
O 1st documented use of insect evidence to
solve crime China in 1235
Insects and Forensics
O Head – brain, antennae, eyes, and
mouthparts
O Thorax – 3 prs. of legs and possibly 2 prs of
wings
O Abdomen – reproductive and digestive
organs
O 29 orders of insects – flies and beetles most
important to forensics
Insect Orders
O Flies – Diptera
- found in almost every environment
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ex) blowflies – found at 1st stages of
decomposition
O Lay eggs in body openings bloated stage
the eggs hatch into maggots move away
from body to pupate beetles move in and
continue decay process
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Insect Orders
O Beetles – Coleoptera
- most prominent in later stages of
decomposition
O Final stage = skeletal – beetles are joined by
other soil-dwelling insects
O See Fig. 12-5 p. 346
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Insects at Work
O Life cycle – egg larva(feeding stage) 
pupa(relatively inactive, nonfeeding stage)
O Abiotic and biotic factors interact to
maintain balance in an ecosystem
O AF = sun, atmosphere, weather
O BF = organisms or remains of organisms
There is strength in numbers
O 1 million species of insects
O Short lifespan but produce large numbers of
eggs
O Contribution to ecosystem = loosening of
soil, pollination, consuming plant pests
O Incomplete metamorphosis –
nymph(wingless) molts several times
adult
O Meteorology vs climatology
Postmortem Interval(PMI)
O Need to establish timeline of events
O PMI is an important element of that timeline
O http://www.pbs.org/wnet/nature/episodes/
crime-scene-creatures/interactivedetermine-the-time-of-death/4390/
Collecting and Preserving
Entomological Evidence
O Include info about rainfall and temperature
O Investigation team collects evidence and sends
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it to the forensic entomologist at the lab
1. Start collection several feet away from the
body
2. measure distance between insect evidence
and body
3. collect samples at all stages on, near, or
under body
4. at lab – raise samples at same conditions as
crime scene
What to record
O 1. temperature
O 2. type and amount of precipitation
O 3. type and amount of light
O 4. humidity
O 5. amount and direction of wind
Temperature
O An increase in temperature = an increase in
insect development
O A)ambient - 1 and 4 feet above the body
O B) soil – surface, 10 cm. below surface, and
20 cm below surface
More on collecting and
preserving evidence
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Nets for flying stage
Pinned or transferred to vial in 80%alcohol
Take 30-60 of largest larvae
Vials labeled inside and out using pencil
a) case #
b) collection time
c) date
d) geographic location
e) location of insects on victim
f) initials of investigator