Forensic entomology

Definition: Application to legal issues of knowledge gained from the study of insects, their life cycles, and by-products.

Significance: Sometimes called upon to assist in legal investigations in both civil and criminal proceedings, forensic entomologists collect insect evidence that may be used to support the cases of either the prosecution or the defense.

Entomology is the study of insects, which constitute the largest and most diverse class of animals in the world. Accounting for nearly two-thirds of all known animal species, insects are found in all terrestrial environments on Earth. Some species even live in the oceans. Insects play vital roles in the health and well-being of many other species of both animal and plant life and thereby help to maintain the balance of life on the planet.

Forensic applications of entomology have long had an important role in both civil and criminal legal cases. Indeed, forensic entomology may be said to go back at least as far as the thirteenth century, when the Chinese scholar Song Ci (Sung Tz’u) commented on the value of evidence from flies in a murder investigation. Xi Yuan Ji Lu (1248; various English translations of the title include The Washing Away of Wrongs and Collected Cases of Injustice Rectified), Song Ci’s treatise on forensic medicine, addressed a case in which a murderer was caught when flies were attracted to the sickle he had used as his murder weapon. However, although the first documented case in which entomology assisted in a death investigation dates back to the thirteenth century, the field of forensic entomology did not become established as a profession until many centuries later and became recognized for its value to forensic science only during the late twentieth century.

Applications in Civil Law

Litigants in civil cases might employ forensic entomologists to inspect shipments of food they suspect are contaminated by insects. In cases in which insect parts are found among food products, one of the first questions that forensic entomologists attempt to answer is when the foreign material was introduced. Whether insect parts were introduced at the time of manufacture, while the food was being stored, or at some moment following delivery can have important legal ramifications. In such cases, forensic entomologists identify the suspected contaminants and try to determine how and when they were introduced into the food.

Forensic entomologists are also sometimes involved in civil cases relating to sales of real property, such as houses that are found to be infested with insects. Again, a primary legal question that is likely to arise in such cases is when the infestations occurred. Cases of that nature require the forensic entomologists not only to identify the species infesting the structures but also to determine all the stages of the insects’ growth and development. To define “infestation” legally, an understanding of the insects’ life cycles is required. Consequently, forensic entomologists must identify and address examples of each state of insect development—from eggs to larvae and adults—to determine how long the properties have been infested.

Postmortem Investigations

Because of the increased popularity of mass-media depictions of death investigations, such as television’s CSI: Crime Scene Investigation programs, many people associate forensic entomology primarily with murder investigations. Trained forensic entomologists do many other kinds of work; however, they certainly do play important roles in estimating the lengths of decedents’ postmortem intervals (PMIs), that is, how long people have been dead. By understanding how insects have been distributed in both time and space, forensic entomologists can often determine where and when crimes have taken place. Their work can reveal when dead bodies have been moved and the seasons of the year within which crimes have occurred.

Forensic pathologists apply a variety of techniques to estimate how long decedents have been dead. For example, they study the stages of algor, livor, or rigor mortis in dead bodies. In cases in which pathologists cannot accurately determine PMI, forensic entomologists can often help. This is because insects frequently invade dead bodies and assist in the decomposition process.

Among the hundreds of insect species attracted to human corpses, the most important include flies and beetles and their larvae, as well as ants, bees, mites, wasps, and other species. Blowflies, houseflies, and flesh flies are particularly well documented as prolific and efficient contributors to decomposition. Indeed, flies are typically among the first insects to arrive on dead bodies. Blowflies often arrive within minutes after death, unless barriers impede their access to the bodies, in which case they may not arrive until several days later. Among the things that impede the arrival of insects are speedy burials; the enclosing of bodies in containers or airtight wrappers; the chemical treatment of remains with insecticides, fertilizers, or bleaches; and even such natural environmental conditions as precipitation and low air temperatures. Flies are typically inactive in rain and fog, at night, and when air temperatures drop below 65 degrees Fahrenheit (18.3 degrees Celsius).

Flies and Decomposition of Human Bodies

Most techniques employed to estimate PMI are temperature-dependent, as warmer temperatures accelerate decomposition and cooler temperatures slow it. Temperature has the same effects on insect activity. Some time after death occurs, adult flies arrive on the body and begin laying eggs. The eggs later hatch into maggots that assist the decomposition process by devouring the dead flesh. Other insects that arrive later may compete with the first arrivals. Knowing the sequences in which the insects arrive and their life cycles can enable scientists to estimate how long the individual has been dead. Because of their predictable behaviors, insect species can provide valuable forensic evidence not only about PMI but also about the causes, manner, and circumstances surrounding human deaths. Such information is deduced from such evidence as the distribution of different insect species on corpses and their chemical makeups.

Because common houseflies feed mostly on vegetation and fecal matter, they are not primary decomposers. They do, however, lay eggs in used human diapers, making it possible for entomological information to be found that may apply to cases involving the abuse of babies and elderly persons. Maggots recovered from used diapers or bedsores can be useful in estimating how long babies and elderly persons have been neglected by those responsible for their care.

In contrast to blowflies and houseflies, which lay hundreds of eggs at a time, flesh flies do not lay eggs. Instead, they squirt out live maggots on the host bodies. Within a few hours, a single flesh fly can deliver hundreds of maggots.

Regardless of whether they emerge from eggs or are born alive, the maggots of all fly species develop through three successive and readily identifiable larval stages, or instars, until they are ready to pupate. During their pupa phases maggots undergo a metamorphosis and later emerge as adult flies. The entire life cycles of flies—from eggs to pupae—are temperature-dependent. Forensic entomologists must therefore not only identify the species of flies recovered at crime scenes but also determine the temperatures and environmental conditions in order to reconstruct accurately the chronology of the insects’ life cycles. Their first objective is to estimate the minimum length of time required for a body to reach its current level of decomposition. That figure is a function of the maximum length of time it may have taken for an insect population to achieve the stage of development found on the body at the time of its discovery.

To determine the lengths of the life cycles of insects found on bodies, entomologists collect live specimens and breed them under carefully managed conditions. By matching the temperatures and humidity levels prevailing at the crime scenes, they can obtain fairly accurate estimates of how long the bodies have been dead by comparing the stages of development of the insects found on the bodies with the stages through which the control samples are developing.

Bibliography

Byrd, Jason H., and James L. Castner, eds. Forensic Entomology. Boca Raton.: CRC, 2000. Print.

Erzclioglu, Zakaria. Maggots, Murder, and Men. New York: Dunne, 2002. Print.

Goff, M. Lee. A Fly for the Prosecution: How Insect Evidence Helps Solve Crimes. Cambridge: Harvard U P, 2001. Print.

Greenberg, Bernard, and John Charles Kunich. Entomology and the Law. New York: Cambridge U P, 2002. Print.

Sung Tz’u. The Washing Away of Wrongs: Forensic Medicine in Thirteenth-Century China. Translated by Brian E. McKnight. Ann Arbor: Ctr. for Chinese Studies, U of Michigan, 1981. Print.