Entomologists and Murder

A forensic entomologist is one who primarily studies insects’ role in decomposition. While they may investigate cases of drugs, toxicity, abuse or medical conditions they usually are asked to estimate the post mortem interval (PMI), or time since death. To do this, entomologists estimate the age of the insects (usually maggots or other larvae) feeding on the corpse. Fly larvae (maggots) will develop at predictable rates under certain temperatures. Generally speaking the warmer it is the faster the development and the colder it is the slower the development. But it is not as simple as that.

The PMI is really comprised of two important parts. The first is the period of isolation. This is the time it takes for the female fly to find the corpse and lay her eggs. Sounds simple right? But the key issue is her ability to find and make contact with the corpse. There are a number of barriers that may prevent her from doing that. These barriers can be both physical (like the body sealed in a car trunk) or environmental (a snow storm). Eventually the female fly may be able to surmount these barriers but it will obviously delay her arrival after death.

This reality can make for an interesting point of conflict in your novel. Say an entomologist estimates the time since death as 4.5 days but didn’t know until trial that the body had been kept in 55 gallon drum for several days before dumping. That might throw the investigation into a bit of a tailspin right? Especially if their main suspect has an alibi for the revised time of death.

The second part of the PMI is the time since colonization. This is the estimate of the age of the maggots. If you are going to get into any details on this process I would suggest that you contact a university entomologist (preferably one who works on forensic cases) and talk to them about the types of flies commonly found in the area depicted in your novel. They might then assist you in creating a realistic time line for the maggot development based on your storyline.