fo-ren-sic: involving the application of scientific knowledge to legal matters.

—Webster's New World Dictionary

 

    

Forensic Entomology

We live in a world populated by bacteria and insects. Although it seems that we spend a lot of effort in fighting them, they provide a useful service as natural rubbish recyclers. Think of that dark brown leaf mould or compost that you find in rainforests. Through decay all the chemicals used by living things are able to be re-used.

Forensic pathologists and entomologists specialise in studying the rates of decay of human remains. By understanding the time and sequence of various stages as bacteria and insects attack the body, they can usually make an accurate estimate of the time since death. This period is called the post-mortem interval (PMI). In addition, many different species of insect attack a corpse at different stages of decay and even prefer different tissue types (such as a beetle which attacks bones). One species, the cheese skipper larva (Piophila casei), is found in dead creatures only after about 2 months has passed. Since some insect species are only found in certain geographical regions, climates or locations (eg swamp or desert), the police can work out if the body has been moved from another location.

'Shou' means 'long life' but ...

The earliest account of someone using insects to solve a murder comes from Ancient China. A peasant had been hacked to death. The investigator, Sun T'zu, asked all the villagers to bring their harvesting sickles and lay them on the ground. Neighbourhood flies that could sense odours not detected by humans, settled on one of the sickles that contained small traces of human tissue. Thus the murderer was identified and he confessed his crime.

Activity

Print out the worksheet for this topic.

Go  to the Forensic Entomology Pages International using the buttons below.  Read the articles in order to answer the questions on the sheet. (Click your browser Back button to return here or close the window).

Now check out these case histories to look at real examples of forensic investigators in action:

Cannabis seizure in New Zealand

The accused ferry captain

The incriminating ski mask

The case of the blood-stained shirt

KEY IDEA:  Reconstructing a time line

Imagine you come home from holiday to find your home broken into. A window was forced to gain entry then left slightly open. The carpet has a large wet patch directly underneath the window that faces a garden bed. What are your observations and what can be inferred? Since there are no wet muddy footprints anywhere you deduce that the burglar entered during a dry period. Checking with neighbours, you find that it rained twice. The first time occurred a week ago and rain lasted 24 hours. It then rained again last night for half an hour. There is too much water remaining in the carpet for it to be due only to last night's rain, considering the size of the window opening. Therefore you conclude that the break in occurred over a week ago.

Forensic Entomologists use this kind of reasoning to estimate time of death. it is  based on their  knowledge of the different stages of larval growth and which species of insects arrive first or later on the scene, together with environmental factors.

Other Entomology Links:

The following resources also contain links to other sites

American Board of Forensic Entomology

American incidents from the FBI casebook

The Testimony of Bugs

An easy-to-follow account of forensic entomology

Forensic-Entomology.com

Comprehensive site designed for professionals

Agriculture Western Australia: Forensic Entomology Page

Has good pictures of insects and larval stages in the insect life cycle

Grubs, Cubs and the Law

Scientific American article about forensic evidence used to convict Canadian bear poachers