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The maggots of all fly species develop through three successive and readily identifiable larval stages, or instars, until they are ready to pupate. It is during the pupae phase that the maggot undergoes a metamorphosis and later emerges as an adult fly. Because the timing of the entire life cycle of the insect (egg laying, hatching, instar development, and pupae phase) is dependent on temperature, the forensic entomologist must not only identify the species of the flies recovered from a body but also record the temperature at the scene and take note of the surrounding environment so that the same conditions can be replicated accurately in the laboratory.

The entomologist attempts to estimate the minimum length of time necessary for the body to arrive at its observed decomposed state based on the maximum length of time it may have taken for a population of insects to achieve the stage of development documented on the body at the time of its discovery. Both living and dead insects are collected at the scene of the body's discovery, and the living insects are then reared in the lab under conditions matching the scene's temperature and humidity as closely as possible, until they reach the stage of development of the insects found at the scene. By noting the time and conditions of the collection of the insects at the scene and by documenting the length of time necessary for the living insects to reach the stage of those observed at the scene, the entomologist can infer how long ago the infestation occurred and thus estimate the postmortem interval.

Forensic Science
Forensic Entomology

Forensic Applications: Time of death determination; suspect identification

Definition: Profession that uses insects and their by-products as evidence to assist in criminal investigations, prosecutions, and defenses.

Significance: Dead bodies attract flies, other insects, and arachnids that can provide valuable forensic evidence in criminal cases involving homicides. Insect evidence is also used in other cases, from civil suits over termite damage to prosecution of poachers who leave animal evidence that gathers insects.

Insect evidence was considered in criminal cases in China as early as 1235 c.e., but the term "forensic entomology" was not applied to the field until 1855. Through the following century, many people doubted that forensic entomology qualified as a science. During the 1980's, however, the area of study burgeoned and gave rise to such professional journals as the Journal of Entomological Science, Journal of Forensic Science, and Journal of Medical Entomology. During the early twenty-first century, forensic entomology became almost popular in the public eye, thanks to its exposure on television programs such as CSI: Crime Scene Investigation and real-life advances resulting from growing knowledge and improved methodologies. In 2001, the highly respected journal Forensic Science International published an issue devoted entirely to forensic entomology.

Uses of Forensic Entomology
The most common use of entomological evidence in homicide or murder investigation is in determination of time of death. Physical changes that dead bodies themselves undergo help to determine the time that has elapsed since death, or postmortem interval (PMI), only within the first forty-eight to seventy-two hours after death. By contrast, insect evidence can establish the PMI after weeks, sometimes even months, have passed. The two primary clues as to time of death are the types of insects present on a body and their stages of development. For example, blowflies find dead bodies quickly, whereas beetles usually arrive much later. Over time, the insects that colonize bodies create sequences of eggs, larvae, pupae, and empty pupa cases. Many insects lay eggs only at certain times of the year, or only during the day or night. Facts such as these can help forensic entomologists establish parameters as to PMI.

Insect evidence can also help to establish certain facts about death scenes. For example, contrasts between the insects found on dead bodies and those native to the places where the bodies are found can show that the bodies have been moved from their actual death sites. Water insects, such as midge larvae, can indicate where, when, and how deeply bodies have been underwater. Because blowflies lay eggs in moist areas, clusters of blowfly maggots may indicate sites of open wounds even after decomposition has blurred evidence in a body's flesh. When the PMI can be accurately fixed, the types and numbers of insects present in a body can show whether the body was hidden in a closed room, buried, or even frozen after death.

Crime Scene Investigation Procedures
Immediately after a person dies, if the body is left unattended, insects will grow and develop on it at a steady rate. Blowflies, flesh flies, and houseflies start to colonize the body almost immediately and begin feeding off it within twenty-four hours unless the body is in a very cold location. These insects lay eggs in moist areas of the body, generally in open wounds, but any orifice may suffice. By examining the insects' stages of growth after a dead body is discovered, forensic entomologists can estimate the time of death with some precision. Knowing the time of death can often play a crucial role in a homicide investigation.

Ideally, forensic entomologists should be called to many homicide scenes to collect insect evidence, but that is often impossible. Because these specialists may be unavailable, evidence technicians must be specially trained to avoid the loss of valuable insect evidence. Insects should be collected from all body parts on which they are found, and every type of insect observed on a body should be collected. Moreover, insects collected from different parts of a body should be packaged in separate, carefully labeled containers. Ideally, two samples of each type of insect should be collected from each area of a body, with one sample placed into a vial containing preservative and the other kept alive for analysis of its maturation process. Forensic entomologists use such samples to estimate time of death.

The development of fly maggots can also be used in the determination of time of death. It takes seven days for maggots to reach their adult stage, and during that period they progress through several stages, each of which can be dated. After one week has passed, however, multiple generations of adult flies develop, making this method of dating useless for estimation of the PMI.

The interpretation of insect evidence in a corpse requires not only detailed entomological knowledge but also knowledge of the local environment. Temperature, for example, can greatly affect insect development, as can the natural insect population in the environment at the time. The findings of studies undertaken by Melanie Archer in 2003 and 2004 challenged the usefulness of insect data because Archer's experiments found unexpectedly wide variations in insect evidence. Most forensic entomologists, however, see these findings merely as a call for more research. Professional entomologists generally do not present only one interpretation of the evidence they collect; rather, they present ranges of possibilities and impossibilities that are often enough to help convict or exonerate criminal suspects.

A well-known laboratory for forensic entomology is the Anthropological Research Facility at the University of Tennessee, which is popularly known as the Body Farm. William M. Bass developed the facility, where scientists study the decomposition of human corpses under many conditions, including the behavior and reproduction of insects on corpses.

Ayn Embar-Seddon and Allan D. Pass

Further Reading
Bass, Bill, and Jon Jefferson. Death's Acre: Inside the Legendary Forensic Lab the Body Farm Where the Dead Do Tell Tales. New York: G. P. Putnam's Sons, 2003. Fascinating story of the research conducted at the University of Tennessee's Anthropological Research Facility.

Byrd, Jason H., and James L. Castner, eds. Forensic Entomology. Boca Raton, Fla.: CRC Press, 2000. Rich collection of essays examines vital issues in the field. Aimed at readers with some background knowledge about insects.

Erzinçlioglu, Zakaria. Maggots, Murder, and Men: Memories and Reflections of a Forensic Entomologist. New York: Thomas Dunne Books, 2000. Collection of case studies offers basic entomological information and discusses how forensic entomology is used, and misused, in court.

Forensic Science International 120, nos. 1/2 (2001). This issue is devoted to forensic entomology, with twenty-five articles by leading experts in the field. Topics range from narrow studies of blowflies to broad surveys of the developing profession.

Goff, M. Lee. A Fly for the Prosecution: How Insect Evidence Helps Solve Crimes. Cambridge, Mass.: Harvard University Press, 2001. One of the leading authorities in the field presents a lively, almost journalistic, account of forensic entomology. Lavishly illustrated.

Greenberg, Bernard, and John Charles Kunich. Entomology and the Law. New York: Cambridge University Press, 2002. Comprehensive scholarly text provides thorough discussion of forensic entomology. An essential work for professionals, but also accessible to novices.

See Also
Animal evidence; Body farms; Crime scene documentation; Crime scene investigation; CSI; Death determination and certification; Evidence processing; Quality control of evidence; Silence of the Lambs.