The entomologist will not be able to give you an exact time of death, but rather an estimate. The estimate will always be a range of time. The range will vary from a few hours to months to years. Thebugs? you find on a dead body can tell a forensic entomologist how long the body has been dead.
The idea behind using insects to estimate a minimum PMI, or post-mortem interval, is based on how insects develop or grow up. Some insects, those with a so called complete metamorphosis, have immature stages whose movement is extremely limited, but have adults that are among the most mobile animals on earth. Some of these insects are specialized to develop on dead animals or carrion, including corpses. The adults fly far and wide searching for a suitable corpse. When they find one they lay their eggs. The eggs develop into larvae, white flabby eating machines that grow by eating the corpse. The larvae cannot move far, and eventually change into winged adults via an intermediate stage called the pupa. Therefore, if one collects an egg, larva, or pupa of one of these carrion insects on a corpse,, this eggs, larvae or pupa had to develop at that corpse and did not come in already formed from somewhere else. If an entomologist knows how long after death the eggs are laid, and how fast the larvae grow, he then has the lenth of time the corpse have been exposed to insects. This length of time is the minimum PMI. So, if all the information exists the entomologists can put it together to obtain a fairly precise estimate of the minimum time the body must have been accessible to insects. For example, let us say that a coroner collects the newly-formed pupae of a particular fly at a corpse. The entomologist knows that this particular fly usually arrives at a corpse within an hour of death, and that the eggs take an average 500 hours to become pupae at the temperature of the corpse. He can then say the PMI was probably 501 hours, and certainly no lower than 491 hours or no greater than 511 hours.
Res Natural The entomologist will not be able to give you an exact time of death, but rather an estimate. ... you find on a dead body can tell a forensic entomologist how long the body has been dead. ... Also, Entomological evidence can help determine the circumstances of abuse and rape. ...