(FEY) Introduction to Forensic Entomology Lesson

Introduction to Forensic Entomology

Insects are among the most common organisms found on Earth. They represent more than ⅔ of all known species! With populations that large, their total biomass is greater than that of the entire human population! With these facts, it is no surprise that insects are found in corpses and play such a key role in decomposition. Insects progress through cycles of change known as Metamorphosis. Metamorphosis is found in both insects and amphibians and is the process of transformation from an immature form to an adult form in two or more distinct stages. Metamorphosis can be either complete or incomplete and involves the change from egg to larva to pupa to adult insect. This same process of change plays out in corpses and carcasses and is an important part of the decomposition process of humans and animals as summarized below.

Eggs are laid in the corpse or carcass by flies soon after the death of the person or animal. The eggs will develop based on the temperature of the surroundings and from the eggs, immature young known as larvae will emerge.

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Larvae are the active, immature form of an insect between the egg and pupa phase. Their bodies are generally soft and tube-shaped. Larvae are also known as "Maggots" and are responsible for much of the decomposition process. They feed voraciously on the flesh of the decomposing bodies throughout their development within the corpse. Larvae are found within a few days after death or exposure to the environment where flies are present.

Pupa, or pupae as plural, is the inactive, immature form of an insect between the larval and adult insect phase. This is the point at which the insect forms a chrysalis, or "cocoon". The hard-shelled chrysalis provides the protection the insect needs during the final stage of metamorphosis. The presence of pupae indicate that the body has been dead for about one week, generally. Other insects, beetles in particular, indicate that the body has been dead for more than one week.

The insect later emerges from the chrysalis as a mature adult insect. This image is of an adult Green Blowfly and is commonly found near a corpse soon after death to begin the cycle as described above.

Forensic Entomology was first described in the 13th century in a Chinese medico-legal text book known as "Hsi Yuan Chi Lu", or "Washing Away of Wrongs" by Sung Tz'u. In this book, he described a case of murder in the rice field in which a worker had been stabbed by a sharp instrument. Sung Tz'u asked all of the workers present that day to lay their tools down on the ground. Soon after flies were attracted to one of the sickles which contained invisible traces of blood from the victim. When Sung Tz'u interrogated the man, he confessed to the crime. Later, Forensic Entomology developed as a scientific discipline in approximately the late 1880s. At this time, Eduard von Hoffman and Hermann Reinhard exhumed numerous bodies and tried to systematically apply entomological concepts to approximate the time since death. The estimates were made based upon observation of the life cycle of flies (members of the Diptera order) within the body. After this massive undertaking, Hoffman and Reinhard essentially became the founding fathers of Forensic Entomology for their tireless efforts to establish Forensic Entomology as valid and useful to Forensic Science. Advances in entomology itself after the second World War resulted in important applications of Forensic Entomology to identify markers of neglect and child abuse prior to death among other advances.

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