The Role Of Entomology In Forensic Investigations

Written by Katherine Steck-Flynn (2003)


This paper is intended for use by police and other emergency personnel who have occasion to be in contact to the recently and not so recently deceased. When first introduced I will mention the scientific name of the various species of insects which colonize bodies after death. After the first mention I will use the common name which is easier to both remember and pronounce.

All too often insect evidence is accidentally destroyed be emergency personnel who fail to realize the importance of this evidence. This author has personally witnessed well meaning emergency personnel shooing away insects and maggots at a scene. I have even observed emergency personnel stomping on maggots as they attempt to flee from the activity around the body. Education in the proper collection and preservation procedures is essential.

Personnel should be aware of the behavior of maggots. They should be able to recognize the types of insects normally associated with a body. They should be able to recognize evidence of insect activity such as beetle frass (Bryd, 2001), and pupal casings (Erzinclioglu, 2000).


Insects (Arthropods) are everywhere. There are so many of them that each species has developed a unique niche in which to breed and feed. This is what the Forensic Entomologist hopes to take advantage of. Each species comes with a unique and predictable set of environmental conditions under which they can and will grow and thrive. To know the conditions in which a particular species will live is to know the history of the corpse they are living on or near.

Insects and the Time of Death Question

When used in conjunction with other standard methods insect evidence can be used to estimate the Post Mortem Interval(PMI). This term is more accurate than referring to ‘Time of Death’ since the exact time of death is difficult to impossible to predict(Erzinclioglu 2000).

The most commonly used and widely known method of determining the PMI is use of temperature readings. Temperature is used to calculate how many degrees from normal body temperature the body has dropped. There are several problems with this method. The temperature of a body is affected by many variables such as the circumstances of death, the environmental conditions, whether the deceased took drugs or whether the deceased struggled.(Baden and Hennesse, 1989) Bodies also cool at various rate according to weight and fitness (Knight, 19??).

The following quote is from Dr. Ian West’s Casebook: The Chilling Investigations of Britain’s Leading Forensic Pathologist.

“Temperature is not as useful an indicator as some people think. It is fine for a body found indoors, assuming the temperature in the house remains constant but for the outdoor scene temperature is notoriously unreliable.” (West and Stern, 1996, p. 231)

Another problem with Temperature, other than the range of variables to be considered, is that each investigator seems to use different standards to estimate the cooling rate per hour. Dr. Micheal Baden, the former chief medical examiner of New York, NY. uses a one degree per hour cooling rate (Baden and Hennesse, 1989). Dr. Ian West uses a formula of 1.5 – 2 degrees Celsius per hour for the first two hours and then .75 degrees after that until the body reaches environmental temperature. Dr. West points out that environmental factors such as rain can greatly affect the cooling rates( West & Stern, 1996). The Encyclopedia of Forensic Science uses a standard of 1.5 degrees Celsius per hour (Lane, 1992).

Once the body reaches environmental temperature the only thing this can tell an investigator is a rough estimate of the minimum time since death. However, anyone who has experienced -40 degrees Celsius knows there are conditions in which cooling would occur more rapidly. The Nanogram developed by Henssage and Madea(n.d.) takes into consideration weight but does not compensate for environmental conditions or the effects of drugs (Knight, 19?? ).

The predictable progression of Rigor Mortis is also used as in indicator of the PMI. Rigor mortis is the gradual stiffening of the muscle due to a build up of Lactic Acid in the muscles(Knight 19??). Rigor starts in the small muscles of the face and progresses to the neck , upper extremities, trunk and lower extremities(Lane, 1992). Rigor alone is also unreliable in that is affected by exertion prior to death (Knight, 19??), body fat(Thomas 1989) , drug use (Baden and Hennesse, 1989) and other environmental conditions. A body may pass through rigor much more quickly than the standard 36 hours according to body fat and other variables (Thomas 1989). There are some medical conditions which cause stiffening of the muscles with no relation to Rigor Mortis (Lane, 1992).

Hypostasis is also used to predict the PMI. Hypostasis is the settling or pooling of the blood due to gravity. Once the heart stops pumping blood will pool in the area of the body closest to the ground. Hypostasis begins to appear 6-10 hours after death and is fixed after 24 hours (Lane, 1992). These rates are highly variable and provide a very short window in which any estimates of the PMI can be made. Hypostasis may not be fixed if the body is moved within the first 12 hours after death (Baden & Hennesse, 1989). Color of the hypostasis may provide some indication of cause of death but in general is also unreliable as a form of estimating P.M.I,(Lane, 1992).

A relatively new method is sampling of the Vitreous Humor of the eye. As red blood cells in the retinal vessels break down Potassium is released as a by product. This potassium accumulates in the Vitreous Humor at a predictable rate (Lane, 1992). This method is considered relatively accurate however the eyes must be intact for this procedure. As well, an advanced stage of decomposition may make this procedure impossible. Finally, in bodies drained off blood or where the body is not intact the rate of break down of red blood cells may be affected.