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."