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Posthumous memoirs

Insects in cadavers contain information that helps to explain mysterious deaths

NegreirosWith a rope around his neck, a youth hung from the kitchen ceiling of an abandoned house in a district in the western part of the city of Rio de Janeiro. He had been dead for a fortnight at least, swore the neighbors. However, the clues analyzed by the Rio police told a different story. The standard tests, which take into account the conservation state of the body, temperature and rigidity induced the experts to place the time of death at only one week. To settle this doubt, the police resorted to Janyra Oliveira da Costa, an expert from the Rio de Janeiro Criminal Institute and a specialist in a field of science that has become fairly well known thanks to American TV series: forensic entomology. At the crime scene, Janyra focused not on the body itself, but on the larvae of flies and beetles on it and on those that were spread over the floor. “The diversity of insects was great, which points to a longer time span since death”, stated Janyra. “As the body remained hanging all this time, it was better preserved than if it had been in a different position”, she explained. Because insect larvae feed on decomposing organic matter, in a sort of natural nutrients recycling system, they fell on the ground rather than remaining on the body. Janyra’s explanation supported the neighbors’ version, causing the police to expand its list of suspects to encompass people who had been at the place sometime in the two preceding weeks.

Working on the identification of the insect species generally found around the dead in the Greater Rio de Janeiro area, Janyra is one of the researchers who in the last few years have been helping to develop this specialization in Brazil in accordance with the country’s predominant fauna and environmental characteristics, which are quite different from those abroad. She has recently tried to incorporate the observation of the presence and behavior of insects into the Rio de Janeiro police routines, since the flies, beetles, wasps and butterflies that make use of the dead to feed their young may help to clarify when, where and how a crime or a mysterious death occurred.

The traditional tests carried out by the medical examiners are useful to clarify complicated cases, but only if performed, at most, within 72 hours after death. Thereafter, their precision drops substantially because biochemical reactions that continue to occur in the corpse suffer the influence of factors that cannot always be identified or controlled. Thus, it becomes harder to conclude what was the cause or date of death. However, with insects things are different. Incapable of controlling their own body temperature, the several stages of their development – hatching of the egg and transformation into a larva or pupa – are controlled by external factors that researchers are highly familiar with: the environment’s temperature and the availability of food.

As food is usually plentiful in these cases, based on the temperature of the corpse and the environment, and once the insect species have been identified, the length of time it took for the insects to reach the stage in which they were found can be estimated, and thus the time of death determined. Soon after death, proteins, sugars and fats in bodies (humans or otherwise) are transformed into volatile chemical compounds, such as alcohols and aldehydes. The acid smell is immediately detected by insects, for which corpses offer an important source of food for their offspring. “The longer the time elapsed, the more insects can help define, precisely, the time since a person died”, states the physician Arício Xavier Linhares, a forensic entomology expert from the Biology Institute of the State University of Campinas (Unicamp).

One of the pioneers of the study of forensic entomology in Brazil, Linhares coordinates a team that includes researchers from the São Paulo State University – Unesp and, since 1991, has been investigating which insect species first reach the body after death and which succeed them over time. It is an exhaustive task in a country of continental dimensions such as Brazil, where insect diversity is great and there is a range of conditions of temperature and humidity, factors that can aid the proliferation of certain species of flies, butterflies and beetles, while hindering the proliferation of other insect species.

In 16 years of work, Linhares’s group found, for example, that flies such as Sarconesia chlorogaster, (greenish with long wings) and Calliphora vicina (black and rounded with dark wings) are found primarily in the south of the country. The former is more common in rural areas and the countryside, whereas the latter is typically urban. However, in the State of São Paulo, the main urban representatives are metallic green blow flies, namely, Chrysomya megacephala, Chrysomya albiceps and Lucilia cuprina. In rural areas or those covered by thick vegetation in the inner-state region, the most frequent flies are Hemilucilia semidiaphana and Chloroprocta idioidea, in addition to species belonging to the Paralucilia genus.

Information about insect populations that are characteristic of given environments (urban, rural, the Mata Atlântica coastal rainforest or the Cerrado savannahs) researched by Linhares’s team are important to determine not only the date of death, but also where it took place. They allow one to assess whether the body was transported, a strategy often employed by criminals to hinder police investigation. “If in the body of a person found in Rio de Janeiro we find the larvae of insects from the São Paulo inner-state area, we can say that the person did not die where the body was found”, says Linhares, whose group has been traveling through the state for almost two years to identify the most commons insect species in the different parts of the state of São Paulo.

At Unesp in Rio Claro (São Paulo inner-state area), biologist Leonardo Gomes, from the team headed by Claudio von Zuben, discovered that the variety of insects that feed on decomposing bodies is far greater than was formerly thought. Gomes worked with swine because of their similarities to humans in terms of size, weight and hair. Every season of the year, he left two animals in open fields and monitored the evolution of insects through morning, afternoon and evening visits every day, starting right after death and continuing until the bodies were totally clean. He found that they were consumed by some 60 species of insects, almost twice the number stated in studies carried out in Europe and the USA.

The commonest flies were Chrysomya albiceps and C. megacephala. Among the beetles, one of the most abundant ones was Necrobia rufipes, only 5 millimeters long, with a carapace ranging from dark blue to black and reddish antennae. “We are bringing to the surface specific details about our setting, where temperatures are higher and the winters are not very severe. That is why we find a far greater diversity than in other countries”, states Gomes, who organized the book “Forensic entomology: new trends and technologies”, consisting of a series of articles that resumes the origins of forensic entomology and discusses its recent trends, to be published this year by Springer, an international publishing house.

Mindful of the climate, Gomes found that in the summer around the city of Rio Claro, corpse decomposition is faster, taking 14 days on average. In winter, when temperatures are more agreeable, the process can take one month. The diversity and quantity of beetles and flies also varied somewhat between these two seasons. In summer, the biologist collected 21,231 insects of 32 different species. In winter, however, this fell to 17,762 insects of 19 species. “The foundation of this genuinely Brazilian data is the key element for forensic entomology to help clarify crimes in this country”, states Gomes.

NegreirosAnother one of his discoveries might provide guidance as to how the investigation of mysterious deaths is conducted. Knowing that insects do not spend their entire lifecycle within the body of the dead animal (once fed, the larvae bury into the soil and undergo a metamorphosis until they reach their adult form), Gomes dug 30 cm deep holes and collected soil samples up to 10 meters away from the pigs’ carcasses. The samples were stored until the insects emerged in their adult form and their species were identified. With these data, Gomes and Von Zuben built a mathematical model that shows that the older larvae, that will become adults first, are generally found within three meters of the body. “Because they were the first to have contact with the body, they offer the greatest amount of information about the time of death”, explains Gomes. “This is the area in which criminal experts should focus their investigations”, he says.

Gomes also noted that here the sequence in which different insect species take over bodies is not the same as in other countries. European and American studies mention seven or eight invasion waves that follow a set sequence. In Rio Claro, however, Gomes showed that this order is not absolutely fixed. In theory, flies come first, in their quest for liquids and tissues in the early stages of decomposition. Beetles appear last, when there are only finer and less fatty tissues left, such as cartilage. Gomes, however, said that “we found at least two beetles, Dermestes maculates and an unidentified species of the Phanaeus genus, that appeared shortly after death”. According to him, this variation changes the understanding of how these cycles follow each other and should be taken into account by experts in their investigations, because they interfere with the estimated time of death.

“Seeing beetles tends to indicate that the person died at least five days earlier. Our data shows that this time span might be shorter”, states the researcher, who in June of this year started to replicate the experiment. This time, Gomes decided to monitor the decomposition of pigs in a sugarcane plantation on the outskirts of Rio Claro. “A lot of murder victims are found in this environment in the state of São Paulo”, he explains. The preliminary results show the importance of examining different environments within a given region. “The number of insects and of species is far smaller in the sugarcane plantation”, says Gomes. Additionally, the occurrence of species varies in a different way in the different decomposition stages.

Recently, Wesley Godoy, a biologist from Unesp in Botucatu and a member of Linhares’s team, confirmed in a laboratory another uncommon insect behavior that could hinder death investigations. He observed that the Chrysomya albiceps fly can become a predator of other insects when conventional nourishment becomes scarce. “When they can no longer find food in the body in an advanced stage of decomposition, the larvae start to attack other species”, says Godoy, who described this behavior last year in an article published in the Journal of Insect Behavior. “As C. albiceps starts to take over, the diversity and abundance of the other insects diminishes and a technician might reach the wrong conclusion about death having occurred just a short while before”, he explains.

In Campinas, Linhares’ group discovered that insects can reveal more than mere details about when and where death occurred. Tests conducted by biologist Patrícia Jacqueline Thyssen show that they can also suggest the cause of death, because, when they feed, the larvae absorb chemical substances from medication or illicit drugs, which alter their development. Patrícia noticed that C. albiceps larvae in general take 96 hours to become adult and fly. When they feed on the body of someone who had used cocaine, however, the time they take to develop drops from 74 to 80 hours. “In an investigation, one can think that this is a mature insect, whereas in reality it’s a young insect whose maturity was sped up. It’s a false clue”, explains the Unicamp biologist. She also found that the opposite can also be true. Larvae that feed on the body of someone who had consumed phenobarbital, the active ingredient in the medication for convulsion and epileptic crises, take longer than normal to develop. Phenobarbital can delay by as much as 72 hours the development of Chrysomya putoria flies and, depending on the amount, it can even kill the larvae.

The toxicological exams of insects can provide more information. Patricia tells us about a recent case handled by the IML (medical examiner’s office) in the city of Campinas. A young man was found dead and even after the traditional investigation there were still doubts as to the cause of death. Called by the medical examiner’s office, Patrícia noticed that some of the larvae on the young man’s body, particularly around the nose, were behaving oddly. They were larger than normal and were more separated from one another. Laboratory tests indicated that they had had contact with cocaine (a suspicion that arose from their quick development and unusual behavior), suggesting that the young man had died from a cocaine overdose.

Besides illegal drugs, the Unicamp teams also studies substances found in medication that can help to identify people who have disappeared, even years after death. “When we find an active ingredient from a certain medication in insects buried around bones and we know that the missing person consumed that medication, we have further evidence to aid identification”, explains Linhares, who plans to make it easier to identify the species to which the larvae belong, since they all look alike, through DNA exams and tests.

According to Brazilian forensic entomology experts, the plan is now to transfer the recent scientific discoveries into the day-to-day work of the experts in the field. In Patrícia’s opinion, the first step was taken in March, when the Brazilian Forensic Entomology Association (Associação Brasileira de Entomologia Forense – ABEF) was established. “We are negotiating a partnership arrangement with the São Paulo Criminalistic Institute to help identify the causes of mysterious crimes”, she says. If this works out, the same collaboration that has been successful in countries such as Germany and the US may be repeated here.

The Project
Forensic entomology: the use of arthropods to determine the time, place, cause and circumstances of death (nº 04/08544-0); Modality: Thematic project; Coordinator: Arício Xavier Linhares – Unicamp; Investment: R$ 487,884.39