What do bugs have to do with forensic science?

Just as flies will flock to a piece of rotting meat left out on the table, necrop­hilous insects, or dead flesh-eating bugs, are often associated with human corpses. Forensic entomology, or the use of insect evidence in both criminal and civil cases, helps police and criminal investigators learn a great deal about what happened to a body.

­The major criminal field of forensic entomology is known as medicolegal entomology. It's also known as forensic medical entomology or medicocriminal entomology because of its focus on violent crime. People working in this field usually attempt to determine several important things:

Bugs found in the orifices of a deceased human body, such as the eyes, nose, ears and mouth, will arrive very quickly. Most insects can locate the smell of dead flesh within a matter of hours after expiration, and some insects, known as carrion insects, live their entire lives feeding on dead flesh and developing more generations of bugs. Adult carrion insects, mature and capable of movement, will fly to the nearest dead body to lay their eggs inside.

­Indeed, the fact that bugs will develop and grow inside a corpse is one of the most important aspects an entomologist keeps in mind when investigating a death. There are generally three stages an insect goes through during its lifetime inside a dead body. The first stage is the egg stage, where the insects are still enclosed within their eggs; the second stage is the larva stage, where the small, white larvae that have just emerged from their eggs grow by feeding upon the dead flesh; and the final stage is the pupa stage, which is an intermediate stage that comes before the insect turns into a winged adult. ­

If an entomologist collects insects from a corpse during any one of these stages -- egg, larva or pupa -- and understands the life cycle of that type of insect, he can determine a fairly accurate time of death. In other words, the entomologist needs to understand two basic facts: how long after death the insect eggs are laid plus the amount of time it takes for the insects to develop. These two facts should give him a good idea of how long a person has been dead.

 

­ You'll find all kinds of bugs at a crime scene, but there are a few that typically show up for a dead flesh party. To learn about the importance of flies and beetles, read the next page.

Many kinds of bugs will flock to a decomposing body, but the most common kinds of bugs found on a corpse are flies and beetles. Flies, particularly blow flies, can find dead flesh within minutes. Fly larvae, commonly known as maggots, do the majority of the eating and are responsible for much of a corpse's decay. Beetles, on the other hand, will typically move in once a corpse has dried out.

When collecting insects, investigators try to locate the largest specimens -- the oldest bugs should give the best PMI (postmortem interval). To preserve the insects, samples taken from the body are placed into containers filled with about 70 percent isopropyl alcohol, the same strength as the rubbing alcohol solution you can buy at the store. The containers are labeled with the date and time of the collection and the part of the body from which the insects were taken. Finally, the investigator either delivers the specimens directly to a specialist or mails the containers expressly for examination.

In a perfect situation, insects can prove an easy tool for uncovering the unknown. For instance, if a person dies of natural causes in a room where the temperature has remained constant and the coroner wants to know the time of death, the entomologist simply looks at the bugs around the corpse and reports the details.

It's almost never that easy, however. Investigators need to take into account a large number of variables when collecting specimens. The temperature of the surrounding area, for example, determines how quickly larvae will grow in a corpse. When a person is murdered during the summer months and left outside for several days, the ambient temperature surrounding the corpse can change dramatically. Certain types of blow flies develop faster during hot weather but development slows down when it's cooler. Bugs found on a body that's been outside for weeks or even months show drastic variations in growth cycles, and an entomologist needs to carefully observe the available specimens to determine a likely range.

 

­ For lots more information on how to catch the bad guys, see the next page.