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Insects in Forensic Science
How bugs Tell Time
HistorySung Tz’u. 洗冤集錄
( The Washing Away of Wrongs):
This was the first forensic case ever reported (1247AD). Death of a farmer was
exposed by blow flies.
History (cont’d)Francesco Redi
(1688) showed that maggots arise from the eggs not meat. He disproved
spontaneous generation.
He used raw meat in his experiment of covered and open jars.
HOUSE FLY BLOW FLY
Life CycleMetamorphosis = transition of
insects from egg to adult.
Larvae or maggot
• 1st, 2nd. 3rd instarPupaAdult
Life cycle of blow fly
How temp affects metamorphosis: egg to adult blowfly
@ 70oF = normal life cycle @ 32oF = paused life cycle @ 90oF = speed up life cycle
OTHER FACTORS
High humidity, uppers (COCAINE), increased 02 will increase
life cycle rate by 1 size
Low Humidity, CNS depressant, and decreased 02 can
decrease speed (by 1 size) too
Blow Fly Egg•Size = about 2 mm•Appearance = miniature rice•Death pheromones draw adult blow fly almost instantly•Eggs laid at moist body openings, eyes, anus, nose, mouth, puncture point(s)•Eggs laid per = 150 – 300•Hatch 8-23 hrs later.
•Temperature, humidity, altitude, microclimate, season, and latitude are all factors in speed of metamorphosis
LarvaeLarvae are also called maggots.
They emerge 8 -23 hours after egg is deposited.
They feed ONLY on moist dead tissue.
Maggots help to decompose decaying matter.
They are a source of food for other animals – birds and other insects. Head region
LarvaeEach instar in a
maggot’s metamorphosis is punctuated by a molt
Adult Blow FlyCan smell death
as far as 10 miles away.
Mouthparts They can’t bite it’s only a“lapping” mouthpart.
Flies taste with their feet as well as their mouth.
Third Instars -> pupaThe third instar eats
voraciously and en masse creating heat.
At the end of 3rd instar, it wanders away from the food source to pupate. To avoid predation.
It burrows several cm.
into the soil and forms the pupa (cocoon).
AdultsThe adult fly is
emerging from the pupa.
The wings/head expand & body hardens
They run and hide quickly.
What feeds on the feeders?
Carrion BeetleFeed on the larvae
of the blow fly.
Sometimes the number of beetles exceed the number of larvae.
WASPS
Feed on adult blow flies, maggots, and carrion beetles but not the corpse
Last to arrive, spiders feed on carrion beetles, and wasps but not maggots or the corpse
SPIDERS
SUCCESSION OF INSECTS
DE
ATH
A
DU
LT B
LOW
FLI
ES
M
AG
GO
TS
CA
RR
ION
BE
ETL
ES
W
AS
PS
S
PID
ER
S
THE END
Arthropods also make a Arthropods also make a contribution to cause of death contribution to cause of death in area of toxicologyin area of toxicology
Arthropods may contain drugs Arthropods may contain drugs or poisons in their bodyor poisons in their body
Dr. Richard Merritt discovered Dr. Richard Merritt discovered super maggots on a corpse. super maggots on a corpse. Person died of overdose of Person died of overdose of cocaine and caused maggots cocaine and caused maggots to feed ravenously and grow to feed ravenously and grow abnormally largeabnormally large
► ttp://www.exploreforensics.co.uk/forensic-entomology.html
Decomposition Stages
1. Fresh (1-2 days) – Adult blow flies, yellowjackets
2. Bloated (2-6 days)- Blow flies, yellowjackets
3. Major Decay(5-11 days)- Flies, beetles, cockroaches, spiders After first three stages, liquid has mostly seeped away.
Biomass also drastically decreases.
4. Post-decay(10-24 days)-Beetles, fruit flies, gnats5. Dry Stage (24+ days)-Some beetles, ants, and flies
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