What if insects that feed off dead tissue could help us solve a disappearance or lead us to a corpse? Despite what TV detective series may lead us to believe, the reality in the field struggles to keep up with the rapid advance of the research. The expertise of an entomologist is rarely sought in a forensic context. However, new applications that, only yesterday, belonged to the realm of science fiction could totally change the game.
Cet article a été publié initialement en français : Police scientifique: éclosion des témoignages d'insectes
Flies are the first to arrive on a cadaver.
No fewer than 50 species of necrophagous insects – those that feed on carrion, or dead flesh – exist in Europe alone. On a single cadaver, between five and 30 types of different insects can be found. These insects can provide a great deal of information that is extremely useful to a police investigation. The presence or absence of certain species on a body is especially helpful for specialists in estimating about the time or place of death or if the body was moved post-mortem. When human remains no longer contain tissue useable for tests, insects can also allow for toxicology analyses thanks to the material they have ingested. This method has even been used for the forensic examination of mummies!
But the most common and best known use of criminal entomology remains dating the body. The usual forensic methods—estimation of body temperature, measurements of rigor mortis and lividity, and biochemical analyses—are no longer efficient after about 72 hours following the death, or when the body shows signs of advanced decomposition. Necrophagous insects and certain arthropods remain effective bioindicators for establishing, more or less accurately, the time of death.
Still, the current method of criminal entomology used for dating cadavers suffers from a margin of error that remains too significant. Until now, the technique has consisted of estimating the age of the insects by comparing their growth to other individuals of their species in the same external conditions. But the temperature, the type of food (tissues, organs, brain) and even the competition between species must be taken into account. Determining these factors is fairly complex and leads to significant margins of error.
A source of growing enthusiasm around the world, research into forensic entomology holds a lot of promise. Damien Charabidze, who heads the Criminal Entomology Lab at the Forensic Institute of Lille (France), feels that this branch of scientific legal expertise is still underused. In France, the number of experts can be counted on one hand. “Forensic research is a victim of its own success. It is advancing faster than the expertise actually used in the field. Investigators and judges don’t know the new methods or don’t think to use them. But a revolution is taking place. New studies will change the game,” Damien Charabidze predicts.
New methods will be more effective, more precise
For the moment, only the biggest criminal cases benefit from the expertise of an entomologist. New methods could, however, contribute to making their consultation systematic. A new method for dating a death yields results that are more reliable and faster to obtain. It consists of using genetic data directly to determine the age of the insects. By grinding up an insect and observing the expression of certain genes, it is now possible to establish its age with certainty. Exit the uncertainty of external factors and the time needed for comparison with other specimens in the lab.
The first serious research work on forensic entomology dates to the 1970s and 80s. Entire aspects of the study of insects in this context remain poorly known. A study on necrophagous beetles, published in open access (in French), laments, for example, the small number of scientific publications available concerning certain species of forensic interest. Damien Charabidze is part of a team working on a computer program of entomological expertise, which will go online in 2014. “This program lists all the information available on an international level and, therefore, lets you calculate automatically and with greater reliability the post-mortem interval,” the researcher enthuses. This will help make the dating of a body even more precise by facilitating the estimation of the time elapsed between the human’s death and the insect’s laying of eggs.
Flies lay their eggs on mucous membranes so that their larvae will have easy access to food.
Knowing the characteristics of each species is crucial for determining at what stage of decomposition of the body the insects arrive. The olfactory tastes are different for each. Flesh flies are the first on the scene. It is the aroma of a fresh cadaver that attracts them and drives them to reproduce. As the cadaver deteriorates, the odors released as a result of chemical reactions evolve; they repel the first species and attract others. Cheese flies, for example, are attracted by the odor of the fermentation of casein between four and eight months. Certain species of beetle, on their side, prefer the ammonia-laden emissions that are produced at an even more advanced stage of decomposition.
When science fiction approaches reality
Pushing even farther the utility of the very personal sense of smell of insects, researchers are already imagining new and potentially revolutionary applications. Necrophagous insects could be used to search for a body. Much like bees that are trained to detect explosives, insects could be used to detect the presence of a cadaver over a relatively extensive zone. Investigators would then “follow” the insects to find the body. “Technically speaking, we’re not far,” Damien Charabidze affirms.
Another possibility comes from the context of ecological research. Experiments have been carried out to evaluate the biodiversity of a region by analyzing the stomach contents of necrophagous insects. These contents provide very useful data for determining the species present in the zone under study. Damien Charabidze suggest another use for this method: “We can imagine that, by using this same method in a zone where we suspect a death has occurred, we will be able to attest to the presence of a cadaver in the area and confirm the death of a missing person, in spite of the absence of a body.”
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