How Insects Solve Crimes

By Chris Williams on August 1, 2011.

Entomologists are specialists who study insects. And forensic entomologists are even more specialized. They sometimes serve as crime scene investigators and use their knowledge of insects and their life cycles to help solve murders. For the most part, forensic entomologists study fly maggots on decaying bodies—not exactly a specialty for the faint-hearted or weak-stomached.

There are many species of flies that lay their eggs on dead bodies. Some, like the blue blow fly, are drawn to a body less than an hour after death. The maggots feed on dead or rotting flesh so adult female blow flies are attracted to decay odors as a place to lay their eggs. The flies’ development time from egg to adult is highly dependent on the outside temperature. Maggots develop much more quickly in the heat of August than they do in November. Maggot size and maturity can give clues as to when the blow flies first found the corpse. By identifying the maggots on a body, forensic entomologists can apply what they know about the fly’s life cycle and habits and can pinpoint the time, and sometimes the location, of the death.

police-tapeWhile flies are the first visitors to a corpse, they are not the last. After the flies, come carrion beetles, then hide beetles, ants, and other scavengers that feed on the dried remains of skin and hair.

Case Study: A plasterer who was repairing a mantel in a home discovered the decomposed remains of a baby’s body. At first, it was assumed that the current occupants of the house were responsible for the corpse. But an entomologist studied the body and concluded that flies, then insect scavengers, then mites, had been working on the body for more than two years. The guilt was transferred to the house’s previous tenants who had lived in the house two years before.

Forensic entomology doesn’t always involve a corpse. Entomologists have been asked to provide expert opinion in various legal cases, too.

Case Study: Police in New Zealand seized 188 kilos of marijuana from drug dealers. They asked entomologists to help them find out where the shipment had originated. The scientists found 61 different species of insects in the marijuana shipment. When they studied where each insect was found geographically, they were able to narrow down the origin of the shipment to an area northwest of Bangkok, Thailand. The New Zealand authorities were then able to add the more severe charge of importation to the charge of possession.



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