When a suspicious death is investigated, the medical examiner usually takes soft tissue samples to test for the presence of drugs or toxins. Because soft tissues decompose quickly, it may be impossible to obtain samples for standard toxicology tests. Insects present on the corpse, however, may provide evidence to whether drugs or toxins played a role in the death.
Because certain insects feed on the soft tissues of the human cadaver, these insects also consume whatever substances reside within those tissues, including drugs or poisons. When human tissues are no longer present, tests on the insects themselves may reveal any illicit or therapeutic drugs or other unnatural substances that were present at the time of death. In some instances, even insect feces or castings can prove the presence of toxins or drugs.
Entomotoxicology, as this branch of forensic entomology is known, effectively began with a case study by J.C. Meyer, published in 1980. In this case, the body of a 22-year-old woman was found, along with an empty prescription bottle for phenobarbitol. The woman had a history of suicide attempts, and had left a note suggesting she planned to take her own life. Authorities suspected she died of an intentional overdose on phenobarbitol. However, her body had been exposed to the elements for two weeks, leaving no usable tissue to test for a drug overdose. Secondary screw-worm maggots collected from the corpse were tested instead, and proved to be full of phenobarbitol. Cause of death? Overdose. Case closed.
Forensic studies on insects can also provide information about toxins in a cadaver, which can help determine where the victim has been. In another interesting case, this one from Finland, insects helped police determine the identity of a victim. Again, the body was too decomposed to provide useful tissue samples, but insects were collected from the corpse. Tests on the insects showed the victim's tissues contained several contaminants, including mercury. The contaminants were not present in these levels at the site where the body was found. Investigators learned, though, of another region of the country where similar contaminants were known to exist. A sketch of the victim was shown to people in the mercury-contaminated community, and the victim was positively identified.
Once forensic entomologists began using insect evidence to gather toxicology data from corpses, it necessitated a new line of research. The post-mortem interval, or time of death, is determined based on growth rates of insects found on the cadaver. How would certain drugs, such as cocaine or heroine, affect the developmental patterns of insects ingesting them?
Dr. M. Lee Goff, author of A Fly for the Prosecution, designed several studies to investigate the affects of different drugs on insect development. Cocaine, he found, gives maggots the munchies. Maggots feed faster, resulting in an accelerated progression through the larval stages of growth. However, the cocaine was metabolized once feeding ended and the fly pupated. Results from such laboratory studies are used to calibrate the developmental timelines of insects collected from cadavers at crime scenes.
- A Fly for the Prosecution, by M. Lee Goff
- Forensic Science, by Stuart H. James and Jon J. Nordby