While other insects may be present on a corpse, flies and maggots are the main ones that are considered when investigating a homicide. This is mainly because they are the first ones to detect a dead body. In his book, Invisible Evidence, Bill O’Brien looks at the science of studying insects and what they can reveal to investigators.
Blowflies and Dead Bodies
Even in a small country such as New Zealand, there are over 50 species of blowfly although not all are attracted to a corpse. The flies settle on a dead body as it is a source of protein to feed their eggs or larvae. If a single species is present it often indicates that the corpse has been found relatively quickly. The presence of several species will point to a body that has been dead for some time.
Blowflies lay their eggs in natural orifices such as eyes, ears, nose and mouth. Other orifices will also be used if the body is naked. Gunshot or stab wounds are extremely attractive to flies. It is common for flies to only lay eggs during sunlight hours.
What does an Entomologist do when Examining the Body
When a body is found, an entomologist will take samples of eggs and larvae and rear these in a laboratory to determine the species and age at which they were found. Some maggots prefer a wet environment and others are carnivorous. Each species will be reared in isolation and may be fed cat food. Investigators will also note the weather conditions and environment in the area where the body was found. The surrounds will be searched for signs of further insect activity.
What can Forensic Entomologists Determine from Insects on a Corpse
Maggots go through three stages of growth which are roughly as follows:
The first stage begins when an egg hatches, and lasts for 24 hours The second stage is the period of active growth and feeding and lasts two to five days depending on the species and the temperature The third stage involves moulting and the maggot moves away from the food source to pupate. For this reason, samples are taken of plants and soil around a body as the maggots may burrow down into the ground
Live specimens are taken to the laboratory and half are killed by immersion in near-boiling water; the others are reared to maturity. The dead larvae are measured and examined to determine their age. When the live specimens mature, a positive identification is made of the species. Armed with this information along with the weather conditions, the amount of sun the body was exposed to and other factors, an entomologist can give an estimated time of death. The accuracy may be out by a couple of days or in the case of a badly decomposed body, a couple of weeks. Even so, a forensic entomologist can provide invaluable information to a homicide investigation.
Flies and maggots are the most common insects to be found on and around a dead body. They often arrive within minutes of death and lay eggs and larvae that feed off the protein in the corpse. Forensic entomologists rear maggots from a crime scene and by doing so, are able to give an approximate time of death.
Reference:
O’Brien, Bill, Invisible Evidence, David Bateman Ltd, 2007