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