Forensic Forensic EntomologyEntomology

a word derived from the Greek words entomon (an insect) and logos

(science).

What can it do at a crime What can it do at a crime scene?scene?

Forensic Entomology can determine…• How long the person has been dead (also

known as the post-mortem interval or PMI) • Whether the body has been moved after

death• What injuries they may have sustained

Invertebrates attracted to dead bodiesInvertebrates attracted to dead bodies

• A dead body attracts a wide variety of insects which use the corpse for food and as a place to lay their eggs.

• Flies usually arrive first to a corpse, particularly the blowfliesblowflies and flesh fliesflesh flies (sometimes within minutes of death).

• The eggs laid by these flies, and the larvae that subsequently hatch and grow on the corpse, can be used to give a minimum

PMI (the shortest amount of time the person can have been dead in order to achieve the observed insect community)

If investigators find larvae that take at least three days to

develop, they can infer that the victim has been dead for at least

three days.

Observation & identification of Observation & identification of correct speciescorrect species

• It is very important that careful observations of invertebrate species around the corpse are made and recorded for identification purposes.

• Quick task…you will see an image shortly which you will have to memorise. You will get 1 minute to observe the image and a further minute to record your recollections afterwards.

The blowfly lifecycleThe blowfly lifecycle

Growth rate for flies is dependent on temperature.

To estimate the PMI, an investigator must know the temperature around the body for the period in question.

Times given in this chart are for 70°F.

• Adult female blow flies arrive within minutes to lay eggs on a cadaver. Each deposits about 250 eggs in the natural openings of the body and open wounds.

• The eggs hatch into first-stage maggots within 24 hours.

• These feed and then moult into second-stage maggots, which feed for several hours, and then

moult into third-stage maggots.

• After more feeding, the third-stage maggots move away from the body and metamorphose into adult

flies.

The blowfly lifecycleThe blowfly lifecycle

Insect successionInsect succession• The principle of insect succession can be used to

estimate the PMI.

• Different species of insects prefer different stages of decomposition.

• As the body decays further, it becomes less favourable to early colonisers and more desirable to other species.

WARNING!WARNING!

Many factors can influence the rate of succession and decomposition including ambient temperature, time of day, season and the situation of the body (eg. covered, submerged, whether located near another corpse…etc)