Forensic entomology is the use of the insects, and their arthropod relatives that inhabit decomposing remains to aid legal investigations. Forensic Entomology is broken down into three different areas: medicolegal, urban and stored product pests. The medicolegal area focuses on the criminal component in regards to the insects that feast on and are found on human remains. These insects are referred to as necrophagous or carrion. The urban area of forensic entomology has components of both civil and legal crimes. The insects looked at in this area feed on both the living and the dead. Investigators are looking at markings on the skin. The markings are caused by the insect’s mandible and can sometimes be mistaken as marks abuse. A forensic entomologist may be called to be an expert witness in a civil case that is for monetary damages. The final area of forensic entomology is stored product pests. This area focuses on insects that are found in food. A forensic entomologist may also be called in as an expert witness in this field as well. They can be called in for either a civil or a criminal case that involves food contamination.
Forensic entomology also helps determine an estimate of how long a person or animal has been deceased or the Post Mortem Interval (PMI). Investigators can determine this from insects by studying the development of the insect. There are certain insects that are specialized to develop on bodies that are decomposing. An adult insect will fly around until it finds a body that is suitable for it to lay its eggs. Once the eggs are laid the developmental process begins. The egg develops into a larva or maggot. Maggots cause most of the body’s decomposition because the maggot will do the majority of the eating. The larva then develops into a pupa, which eventually becomes an adult. The insect can be collected at any one of these stages. There are time ranges for how long it takes the insect to develop from one stage to the next. For example: if it takes an average of 500 hours for an egg to develop into a pupa at a certain temperature, then the investigator can give an estimate of how long the person or animal has been deceased and say with certainty that the length of time is within a range.
The weather has the greatest affect on the accuracy of the process described above. Temperature is the main cause of difficulty because a corpse that has been left out in the summer heat can change dramatically which makes it difficult to identify how long the body has been decomposing. Temperature also effects the growth cycle of certain flies. Warm weather speeds up the process and cold weather slows it down.
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 of corpses. Bugs determine time of death in these cases.
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 article on microorganismal research.