Insects of the dead

Legal entomology… Who, these days, does not immediately think of the CSI : MIAMI serie when hearing this term? However, the study of insects associated with death is much older and recurrent in different civilizations. The oldest known representations of flies have been observed on Mesopotamian tablets over 3600 years old. In Ancient Egypt, the Book of the Dead describes how to repel necrophages and improve the preservation of mummies. The links between death and certain insects had already been established.

Photography of the Book of the Dead in Ancient Egypt

When was the use of insects in the justice system? It can be dated to the 10th century in China. Many flies were found on the head of a victim after a fire. This caught the attention of the investigators, who then exposed a major wound, concluding that it was a homicide and not an accidental death. For a long time, despite numerous illustrations of bodies colonized by larvae, no relationship was made between them and the laying of flies. This is the time of "spontaneous generation". It was thought that when a living being died, the insects present during the degradation of the body were spontaneously generated by this same body. This obviously proved to be false, and it was the Italian physician and entomologist Francesco Redi who was the first to refute this theory in 1668.

When did the first forensic assessment take place? In 1855, a study of scavenger insects taken from the mummified body of a newborn baby discovered in the mantle of a chimney during work was carried out by Doctor Berget d'Arbois. He was able to demonstrate that the infant died two years ago. This made it possible to exclude the occupants then of this accommodation where the chimney was. Subsequently several scientists have followed one another: Camille Hyppolyte Brouarde, Professor Perrier, Doctor Reinhard… In 1894, it was Jean-Pierre Mégnin veterinarian of the Armies who, with his work "The fauna of corpses: Application of entomology to forensic medicine", officially gave a name to this scavenging fauna. He will also be the first to evoke a phenomenon of succession of several waves of insects on a corpse. In other words, insects do not all arrive at the same time: each genus, each species are representative and are specific to a stage of decomposition of a body.

Photography of Jean-Pierre Mégnin's book from archives, La Faune des cadavres: Application of entomology to forensic medicine

Thanks to all these major advances, it was at the end of the Second World War and in the United States that modern legal entomology officially joined the criminal sciences.

But who are these death bugs? A lifeless body is quickly visited and colonized by numerous invertebrates. They can be classified into four categories: scavenger species, which feed directly on the corpse; necrophilic, parasitic or predatory species of necrophages; omnivorous species, those that feed on both animal and plant matter; and finally the opportunistic species which use the corpse as an extension of their habitat.

There are approximately twenty-six families of scavengers. Some only feed while others also breed there. These are the ones of particular interest to forensic entomologists (people studying legal entomology). The first group to be found on a body mostly represented are the Diptera.

Photography of a larva (1) and an adult (2) of the Diptera group of the species Chrysomya albiceps (Wiedemann, 1819).

This group includes, among others, certain species of flies. There are also Coleoptera, one of the largest families of insects. In the case of legal entomology, the size of those present on corpses varies from 2 to 4 mm to reach a maximum of 12 mm. They are almost always covered with hair. These species feed on dry tissue.

Photography of Dermeste undulatus (Brahm, 1790) from the Coleoptera group.

Another group that can be found on the corpses: the Lepidoptera.

Photography of Tineola bisselliella (Hummel, 1853), from the Lepidoptera group.

When a living being dies, it stiffens, cools to reach room temperature, becomes dehydrated and acidified. Different molecular processes inside the body then take place, causing the destruction of cells. Insects are attracted to decaying odors, odors filled with molecules which, at the start, are not even detectable by humans. This mixture of molecules varies according to the stage of decomposition until skeletonization and thus attracts different species of insects throughout the process.

This colonization of the body depends on several factors: the body itself, the geography where it is located or was located, seasons and environmental parameters (heat, rain ...). There are eight waves. The first colonizers intervene when the smell is not yet perceptible. We find our dipterans there. The second takes place when the smell is noticeable. You can find Calliphoridae and Sarcophagidae (Diptera). The next phase is particularly fragrant because of the fermentation of body fat. It is then that for this third wave, beetles of the genus Dermestes and small Lepidoptera of the genus Aglossa arrive. There follow the other waves made up of different species acting in a coordinated fashion.

Legal entomology is a complex science with many parameters to take into account and which can change from one environment to another. However, in France, the service dealing with this area is not confined solely to dating the dead. Forensic entomology also makes it possible to act for the protection of species, to carry out a search for responsibility and swindle, but also to deal with health problems and entomotoxicology. That is to say, the search for chemical substances accumulated during the development of the insect on a body that hosted these substances.

References :

1.     Berget, 1855.

2.     Dorothy E. Gennard, Forensic Entomology, Wiley-Blackwell, 2007

3.     Georges P. Yovanovitch, Entomologie appliquée à la médecine légale. Librairie Ollier-Henry, 1888

4.     Greenberg & Kunich, 2002.

5.     J.- P. Mégnin, La faune des cadavres : application de l'entomologie à la médecine légale. Encyclopédie scientifique des aide-mémoire, Masson et Gauthier-Villars, Paris, 1894.

6.     Szpila K. et al. Chrysomya albiceps (Wiedemenn, 1819), a forensically important blowfy (Diptera: Calliphoridae) new for the Polish fauna. Polish Journal of Entomolgy. 2008

7.     Wyss & Cherix, 2006.