As if death weren’t creepy crawly enough on its own, often crime scene investigation involves using insects and arthropods to make forensic determinations at scenes that involve a dead body. Forensic entomologists use the presence of insects to help determine approximate time of death on corpses.
How can insects tell us time of death? Forensic entomologists use two main methods to evaluate approximate time of death in, one method looks at what type of insects are on and in the decomposing body and the other uses the life stages and life cycles of certain insects to establish how long a body has been dead. Which method an entomologist uses is largely determined by the length of time the body has been dead. If the body is suspected of being dead less than a month then the life cycle of insects is looked at and if the body is suspected of being dead from a month to a year then the succession of different insects is looked at.
When a body dies it goes through a number of physical and biological changes; a dead body is said to be in different stages of decomposition. These different stages of decomposition attract different insects at different times. One of the first insects to settle into a freshly dead body is the blowfly. Blowflies have a number of different life cycles starting with an egg stage, moving onto three different larval stages, and going through a pupa stage before emerging as an adult. Because of the extensive study of blowfly life stages and a working knowledge of the length of the each life cycle a time of death, to within a day or so, can be determined from the stage of blowfly colonization on a body.
After a body has been dead for a longer period of time other insects besides blowflies are also attracted to it. With the changes of the body come changes in insects that preferentially feed on it. Blowflies and houseflies come within minutes of death, others come mid-decomposition to feed on the body, while others come just to feed on the other scavenging insects that have inhabited the body. Generally, time of death can be determined by the kinds of insects that are colonizing the body at a specific time.
Scientists are also trying to use this type of successional development to evaluate the time of death using microorganisms, many of which are responsible for decompositional changes, that develop on a dead body . For more information check out this articleon microorganismal research.