Forensic Entomology

(In part, from a Lecture by Dr. Michael Weiss - Department of Entomology)

Insects and Murder

I bet you never thought that insects could detectives and coroners of the world, but there are many examples of how insects have helped solve crimes. Some insects act as scavengers and decomposers, providing a service like the garbage man. As an example, can you recall a road-killed animal after about 2 or 3 days? Although maggots may not be beautiful, they help clean up environment and provide a valuable service by recycling nutrients. They can also provide valuable information to help solve crime.

"The life cycle of blow flies [was] the key to our investigation of the body of a thirty-seven-year-old male, found by joggers in a swamp on windward side of Oahu. the corpse was infested with maggots of two species of blow fly. Our analysis of the larvae, compared with both laboratory-rearing data and results of decomposition studies, suggest the victim had been dead for roughly 120 hours. That conclusion was corroborated by information obtained independently by the Honolulu police: the victim had last been seen alive 123 hours before the discovery of he corpse, and he had failed to report to work 121 hours before his body was found. Our estimate helped place the victim in the company of the suspect, who was later convicted of the murder(Goff 1991) ."

The major group of insects that feed on dead animals are flies and beetles. Forensic entomology is not just used in gruesome cases, it is the general use of insects and other arthropods in legal issues. It can include; urban arthropod pest issues, stored-product arthropod pest issues, and medical-legal issues.

Why Use Insects?

Insects are usually the first animals to find and colonize a corpse. Blow flies will usually oviposit within the first few hours of death. With the passage of time, a series of insects arrive and depart from the corpse. Insect fauna associated with a corpse usually follows a predictable successional sequence. By identifying the insect(s) present and their life stage, it is often possible to estimate how long the body has been dead, and where death occurred.

Succession of Insects

There is a natural succession of insects on corpses. All insects have a niche which is a place in time and space for which they are best suited. For example, one species may be best suited to feed on a freshly killed corpse and another species may be best suited to feed on corpse that has been dead for two weeks. In some situations, one species "prepares" the animal for the next species. This succession of insects on the corpse allows you to estimate how long the animal has been dead, if you know the succession of the insects on corpses.

The Succession of Decay in the Corpse

The corpse goes through four stages of decay.

First is the fresh stage which begins at death and continues to the early stage of bloating. Depending on temperature it can last from 1-3 days.
Second is the bloated stage which begins at the onset of bloating and lasts until cessation of bloating.
Third stage is the decay stage. It begins when bloating has stopped and the remains are relatively dry.
The final stage is the dry stage and it is characterized by the small amounts of tissue that are left.

How do Insects Help Solve Crime?

Predict time of death

Insects are dependent on temperature of their surroundings for development. The warmer it is, the faster they develop. Below certain temperatures they stop growing entirely. If we know how fast an insect develops at different temperatures and if we know the temperatures where the body was found, the forensic entomologist can predict back to the time of death.

Time of year

Insects have cyclic life cycles and are found only at certain times of the year. This can be used to determine if the body has been removed. For example, if you find a corpse in an abandoned house in North Dakota in December with blow fly larvae feeding on the corpse. Wouldn't you suspect that the body had been moved from a warmer location where the flies were active?

Insects can bio-accumulate

As insects feed on a corpse, they ingest and bio-accumulate chemicals that may help solve crime. Maggots have been shown to accumulate detectable levels of phenobarbital, opiates, and other chemicals when they can no longer be detected in the body.