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Investigator's Toolbox

Forensic Entomology: A Bug's Story
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For hundreds of years, investigators knew that maggots swarming on the soil meant a corpse was probably buried nearby. But they considered the bugs a nuisance, a disgusting but necessary part of the job. In the mid-1980s, though, these insects emerged as valuable forensic clues.

Around 1985, scientists started wondering what information insects provided about a victim's time of death. Bugs are, after all, some of the first to arrive at the crime scene. The science of forensic entomology, or medicocriminal entomology, grew out of this new respect for arthropods.

One of the main ways coroners determine time of death is by measuring a corpse's body temperature. Once someone dies, his or her body cools from its live temperature of 98.6 degrees. The longer the person is dead, the more the body assumes the surrounding temperature. This can tell investigators a lot, as long as the cadaver is found within 48 hours. But what about human remains found weeks after death? Enter forensic entomologists, who can apply their knowledge of insects to help investigators unravel a crime's timeline.

We all know that many insects are carrion feeders. As part of their job in the ecosystem, these arthropods dispose of dead vertebrates, including humans, by eating their bodies.

Ever wonder how insects know where to find food? As a corpse begins to decay it gives off an odor. This may smell foul to the living, but to many insects it's a chow call. Insects of the Diptera order (which includes mosquitoes, flies and gnats) usually arrive first in the form of blowflies (Calliphoridae). Flesh flies (Sarcophagidae) come as well.

When they arrive at a corpse, the flesh flies deposit their larvae. Meanwhile, the blowflies lay eggs in the body's orifices and open wounds. Thus, a new arthropod life cycle begins within the cadaver.

Sometimes within hours, the blowfly eggs hatch into larvae, which live on the dead tissue. Over time, the larvae molt and transform, going through several stages, or instars, until finally reaching maturity. The precise time of these changes depends on the species, as well as the temperature of the surrounding environment.

But when biologists know the life cycle of these carrion bugs, they can tell how long the insects have been in the body. Determining this length of time can further indicate the estimated time of death. For instance, blowflies generally start laying eggs within 48 hours of a death. Their eggs become larvae within 16 and 25 hours, and the larvae become pupae within six to 12 days, depending on several variables.

Other species become important as time passes. Eggs of the cheese skipper (Piophila casei) show up three to six months after a victim's death. Beetles that thrive on bones arrive after the bone is exposed. Other beetles begin preying on the maggots feeding on the flesh. In all, it's a complex ecosystem that will generously betray its secrets to the informed entomologist.

Insects can also help investigators establish if a body has been moved after death. Entomologists will check the type of insects within the corpse to see if they are local to the area. If the bugs are foreign to the place in which the body is found, investigators know that someone moved the body after the victim's death.

So watch your step. You may just overlook your most important clue.

Pictures: B. Borrell Casals/Frank Lane Picture Agency/Corbis |

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