Forensic Anthropology
Measuring Bugs
A forensic entomologist specializes in the developmental stages and behavior of different types of insects found on a cadaver at a crime scene. They provide indicators about the time that has passed since the person's death (PMI), although this is not an exact science. They also indicate something about the climate and locale in which the death may have occurred.
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William Bass III |
A prominent physical anthropologist who developed expertise in entomology is Dr. William K. Bass III, who runs the Anthropological Research Facility at the University of Tennessee at Knoxville. This two-and-a-half-acre field is dedicated to the study of decomposing human remains, and the presence of more than a dozen bodies at any given time exhibits their ongoing projects. The facility---dubbed the Body Farm by the press--- has made important contributions to estimating the PMI in suspicious deaths.
Bass, an expert on skeletal identification, pioneered this unusual research over thirty years ago when he discovered that the field's state of the art was "mostly anecdotal." Moving to Tennessee in 1971, he got involved in cases where corpses were infested with insects. "Half of my first ten cases were maggot-covered bodies," he recalls. "I didn't know much about that, so I looked through the literature on the subject, and there wasn't much there."
He soon acquired a field and the unclaimed cadavers of several homeless men. As they lay exposed, they provided information about what happens to bodies under various conditions. Insects came in and became the subject of intensive study.
"Before our work, no one had ever established a time line," Bass points out. "There are many factors that can affect how a body decomposes, but we found that the major two are climate and insects. When a person dies, the body begins to decay immediately, and the enzymes in the digestive system begin to eat the tissue. You putrefy, and this gives off a smell." That attracts the bugs. Measuring and recording this information gave the facility its raison d'être.
As law enforcement realized the value of this information, increasingly more entomologists got involved. M. Lee Goff, professor of entomology at the University of Hawaii at Manoa and author of A Fly for the Prosecution, is a consultant to the Honolulu medical examiner. His book spells out the many contributions that an entomologist can make in a death investigation.
"Most frequently the forensic entomologist is asked to estimate the postmortem interval based on insect activity," Goff points out. "This is actually an estimate of the period of insect activity, not the actual postmortem interval. The two are often quite close, as the insects arrive and begin their activity shortly following death. In some instances, there may be factors that serve to delay the onset of insect activity, and these must be considered."
Other contributions include:
- Determining if the body has been moved following death
- Assessing wounds in terms of before, during, or after the death took place
- Individualizing a crime scene
- Serving as alternate specimens for toxicological analysis
- Providing DNA materials from the gut contents of parasitic insects
- Documenting periods of abuse and/or neglect in children or the elderly
- Supporting or contradicting an alibi
Goff's first experience at a crime scene was in 1984 with the discovery of the body of a female in Hawaii's Hau Tree Park area, located in Ewa Beach. "I had previously participated in a number of cases at the morgue, but this was the first time someone got me out of bed to go to a scene." Since then, he's been increasingly more involved.
In the case of one victim who appeared to have been dead for at least two weeks, the insects had done quite a job. Goff and his assistant collected the specimens and took them back to his lab. They found three species of maggots in different stages of development, which they measured and preserved. They also put some into a rearing chamber to complete their development into adults—thereby differentiating them more definitively. Collecting evidence of one more fly species and two types of beetle, Goff put all of this information into a computer to see if a program that he'd developed would provide a PMI.
The analysis disappointed him: Either no such body existed or there were two different bodies. "In trying to analyze what had gone wrong," he says, "I had to reevaluate the data I had provided to the computer. That led to the discovery of the role that the positioning of the body played in altering the insect activity---particularly the Sarcophagidae larvae." In other words, while it is generally the case that two species would not be on a corpse in the specific stages in which they were found on this one, there was something unique about the crime scene. Goff returned and saw that the victim had been partially submerged, which meant that the flies that might otherwise have left as tissues lost moisture had remained. That was a lesson about the limitations of databases: Any given case may have distinct characteristics that throw the data off.
As time passes, different groups of insects come and go in the process of assisting corpse decomposition. As each feeds on the body, it changes the body for the next group, which is attracted to those particular changes.
Entomologists agree that there are four main types of direct relationships:
- The necrophagous species (flies and beetles) that feed directly on the corpse, and their stages of development over about two weeks helps to indicate how long the person has been dead.
- Predators and parasites of the flies and beetles (other types of beetles that prey on eggs and maggots). One type of blow fly can feed on either body tissue or maggots. Wasps are also parasitic on the maggots, and since they tend to specialize, it's easy to tell what kinds of flies had been on the body.
- Wasps, ants, and beetles that feed on both the body and the maggots. (Wasps that capture too many flies can actually delay decomposition).
- Spiders that use the body as a habitat to prey on other insects.
"The relationships of the insects to the body, in terms of how they make a living," Goff explains, "are determined by the biology of the insect. Parasites remain parasites, although in some cases the tissue-eaters have been known to switch to predation as the body is consumed. Yet habitat and climatic factors can alter their periods of activity on the body. If the particular insect feeds on dried tissues, it may appear earlier in a hot, arid habitat and possibly not appear at all in a moist habitat. These changes may affect the pattern of succession, but the roles of the individual insects are set by their evolution."
The job of the forensic entomologist is to interpret these various relationships in order to offer information to law enforcement officers that will assist in leads. "At present," says Goff, "entomology is relatively well accepted by crime scene investigators. When I first began, we were regarded as having limited value. Over the years, with educational outreach and careful work, we have become a recognized discipline."
For research---since there's only one Body Farm at this time---he relies on pigs. "I have selected sites for my studies based on the records of localities in which bodies have been encountered. For each study, I use three pigs. One is placed directly on the ground, or on whatever substrate I'm investigating. This pig is left undisturbed for the duration of the study. A second pig is placed onto a welded wire mesh weight platform. This pig is used to determine the rate of biomass removal by weight and will be weighed each time the site is visited. It's also equipped with thermocouple probes inserted into the mouth, abdomen and anus to determine changes in internal temperatures related to decomposition. The third pig is also put on a welded wire mesh platform placed directly on the substrate. This pig serves for sampling of insects and other arthropods. Equipment for recording climatic data is placed at each site, including rain gauge and hygrothermograph."
They then record all factors and add their results into an expanding database.
What Goff finds satisfying about this work is its immediate and practical application. "In many of my academic research projects, I never see any application of the results. Here I see an actual situation and a resolution. I must admit to a certain level of excitement in participating---I'm only human---but I never allow this to interfere with my objectivity."
In 1984, he and several other forensic entomologists began meeting informally, and eventually they decided to form a certifying board. "We modeled ourselves after similar boards in anthropology, odontology and pathology. It was finally incorporated in the State of Nevada in 1996 as the American Board of Forensic Entomology."
In the future, Goff believes that advances in technology will make a significant contribution to the discipline. "For example," he says, "the use of DNA technology to identify immature specimens and extract material from gut contents to allow for individualization of both suspects and victims. Also, we need to focus on standardizing techniques for determining basic life cycles. At present, the data are quite varied, leaving gaps when cases come to trial. Yet even within the relatively new area of drug detection, there have been improvements that allow for more precise analyses. I think it's going to get even more exciting in the relatively near future."
Forensic anthropologists appear to have a considerable range of skills for assisting in death investigations. From art to bugs to bones, they make their mark.
