Entomology

Entomology is the study of insects and their life cycles. Many insects live and feed on dead flesh, which is why entomology is relevant to forensic science. The forensic entomologist can help estimate time of death by looking at which insects are present on a corpse and where they are in their life cycle. Entomology can also shed light on the nature of injuries, whether a corpse has been moved, and whether drugs were involved in a death.

A newly deceased corpse attracts flies. Within minutes of a death, blowflies will start to lay their eggs in moist areas such as the nose, mouth, armpit, groin, or open wounds. The eggs hatch into larvae or maggots within 24 hours and these grow to around half an inch in length after about three days. Then, over the next six to ten days, they will develop into pupae with a hard outer case. Adult flies emerge about twelve days after this. If the corpse is not recovered by this time, the life cycle repeats itself so that flies at all different stages of development may be recovered from the corpse.

The forensic entomologist can use the life cycle of the flies found on a corpse as a kind of clock, giving the minimum time that elapsed since the time of death and the time of discovery. If eggs are found, it suggests death occurred less than 24 hours before discovery. The presence of maggots indicates the death occurred less than ten days ago. Pupae and mature flies will suggest a time of death one to three weeks before discovery of the corpse. However, the life cycle of flies is not an accurate clock. Flies are cold-blooded and their activities are dictated by the weather. Maggots may become dormant if it is cold and flies do not lay eggs at night. If someone is killed at midnight, flies will not appear till daylight, which means time must be added to the estimated time of death.

Because flies feed on human tissue, their own tissue can sometimes be used to measure levels of any drugs that may have played a role in the person's death. This is useful when the corpse itself does not yield tissue for analysis. Insect ecology varies from place to place and sometimes the species found on a corpse are not native to the place where the corpse is found. This may indicate that the corpse was moved after death. Furthermore, flies feed on open bleeding wounds and their presence may help distinguish between ante-mortem and post-mortem injuries.