An Introduction to Forensic Entomology: Insect Detectives

Maggots: flash a photo of the squirming larva to nearly anyone and you can expect a disgusted grimace. Show the same photo to a forensic entomologist and prepare to learn. Flies, beetles, and their larva hold key secrets of the corpse upon which they gather. By studying these insects and their larva, the forensic entomologist uncovers those secrets. Forensic entomology, as unpleasant as it may seem, helps the dead tell their tale.

The study of insect activity on cadavers yields important clues about the date and the location of death. Determining the date and location are very important to homicide investigations; knowing when and where a person died can mean the difference between solving a crime and watching a case grow cold. Proving where and when a victim died can help lead investigators to the murderer and/or assist in convicting (or releasing) a suspect.

In fresh homicides, a formula is used to determine the amount of time that has passed since death. Body temperature falls at a rate of approximately 11/2 degrees per hour. Variables that can affect rate of temperature loss (for instance, ambient temperature and body size) are also considered. Along with noting the core temperature, analyzing the progression of rigor mortis as well as other changes (changes that occur at specific rates after death), helps establish an approximate time of death.

Frequently, significant time has passed before a body is discovered. In these instances, a forensic entomologist will often be called upon to investigate any insects or pupae that have been discovered on or near the body.

Blow flies are particularly well-regarded in forensic entomology because they arrive early to the scene and go through a somewhat predictable life cycle. Their early arrival (weather withstanding) makes it easier to follow a time trail backwards to the day of death. Other flies appear later when the body has further decomposed. Also, blow flies are particularly attracted to bodily openings and to blood. Maggot activity in areas that are not natural body openings can indicate perimortem wound sites

Flies are not the only insects attracted to corpses. Some species of wasps, beetles, and mites are also present. Some feed on fly larva. Others feed on the corpse directly, but all insects provide investigators with important information regarding date of death. Furthermore, different insect species live in different regions. If non-native insects are found on or near a body, this alerts investigators that that the decedent may have died elsewhere.

The forensic entomologist will study the adult insects, the larvae, and the pupal casings that have been found at the scene. They will note the development and growth and will apply a formula to determine the days since death. Temperature plays a very important role in the life cycle and, therefore, weather conditions are carefully noted when making a determination.

However, there is another very important factor forensic entomologists must consider: maggots generate heat. Groups of maggots can experience accelerated development due to the warmer temperature generated by the maggot mass. Susan Gruner, a student researcher with the University of Florida, and Dan Slone, an ecologist, conducted a study of blow fly maggots and the heat they generate.

The results of their study were published in May 2007 in the Journal of Medical Entomology. You can read an article about Susan Gruner and Dan Slone's study by visiting the first link supplied in the sources section of this article or by clicking the first link at the end of this article.

Forensic entomology is a fascinating and growing science. This article is only a snapshot of forensic entomology and what forensic entomologists do; I hope, however, that this has given you a better understanding of insects and their importance to forensic science.

If your interest has been piqued, you may find the following resources helpful:

http://news.ifas.ufl.edu/story.aspx?ID=1241

http://research.missouri.edu/entomology/index.html

http://www.forensicentomology.com