Catching Criminals with Bugs

Forensic Entomology - How it Works

Mar 23, 2009 Karen Lotter

Creepy crawly bugs are put to good use by forensic entomologists, who use flies and beetles to help law enforcement officials catch criminals.

Medico legal forensic entomology, which is what people usually see in Crime TV shows, deals with information insects provide in severe criminal cases like murder, suicide and rape. This category of forensic science also includes physical abuse and contraband trafficking, where forensic entomology is used to good effect.

A Good Definition of Forensic Entomology

There are many definitions of forensic entomology, but a good one is that it is the application of insects and other arthropods to legal issues. This includes the study of industrial and urban issues.

The Decay Process- the Role of Flies and Beetles

A wide variety of insect species is attracted to decomposing remains and plays an active role in the decay process. Two groups, the flies (Diptera) and beetles (Coleoptera) are of major importance when looking at forensic entomology.

Flies (Diptera), whose larvae are capable of living in a semi-liquid medium, are the first insects to be attracted to and to colonize decomposing remains. The fly larvae (maggots) are responsible for the dramatic consumption of the corpse's tissues. The other insect groups like the beetles only appear much later to do their job once the remains have dried out.

First on the Scene – The Blowflies

One of the first groups of insects that arrive on a dead human body is usually blowflies. The female blowfly lays eggs within two days after death occurred.

Flies can be found as:

Eggs (in egg masses usually)
Larvae or maggots (in a range of sizes from 1-2 mm to 17 mm)
Pupae and/or empty pupal cases
Adults.

Because it is known how long it takes to reach the different stages in an insect’s life, forensic etymologists can calculate the time since the egg was laid.

Maggot Masses Generate a Lot of Heat

With maggots, crime scene technicians usually collect a range of sizes. Maggots will be found crawling on or near the remains and may be in clumps, called maggot masses. The masses generate a lot of heat, which speeds up development. Therefore, it is important for the CSI technicians to note:

the site of maggot masses
the temperature of each mass (thermometers can be acquired cheaply at drugstores) or if no thermometer available, please estimate size of mass.
to carefully label, which maggots come from a particular mass

All these calculations and notes as well as the age of the insects collected by the crime scene technicians can be considered as an estimate of the time of death.

Other factors that are taken into consideration is temperature, weather, whether the corpse is exposed or immersed in water or buried and the fact that insects lay eggs on bodies any time within two days of the corpse being available to insects.

Other Uses for Insects in Forensic Entomology

There are often instances where the insect itself is the cause of death. There are unfortunate cases where insects have been used as murder weapons, such as locking a child in a room full of wasps.

Maggots have another use. They can be used by forensic scientists as poison detectors. There are times when it is impossible to sample the stomach contents or blood composition of a deceased person. Forensic entomologists can analyze the skins from pupae and dead larvae for the chemicals. They will also take special not because certain poisons affect larval growth.

Sources:

Journal of Forensic Science. Six Forensic Entomology Cases. Mark Benecke, (1998).

Forensic Entomology, the Use of Insects in Death Investigations. Dr. Gail S. Anderson School of Criminology, Simon Fraser University. BC, Canada (1998).

The copyright of the article Catching Criminals with Bugs in Forensic Science is owned by Karen Lotter. Permission to republish Catching Criminals with Bugs in print or online must be granted by the author in writing.

Adult Blowfly