A Moment of Science

Maggots: an Investigator’s “Star Witness”

Grisly as it sounds, by surveying the insects in and around a corpse, forensic scientists can help determine how long ago a victim was murdered.

A large group of maggots devouring a dead possum

Photo: OakleyOriginals (Flickr)

When someone dies outdoors, the first investigators on the scene are usually bright green-bottle blowflies. Attracted by the smell of decaying flesh, these usually arrive within ten minutes of the death.

If you picnicked in a certain wooded lot at the University of Tennessee, you wouldn’t be alone. Dozens of other people are there, and millions of tiny picnickers. Don’t expect good conversation, though, because the people are all dead, and the picnickers–innumerable microbes and insects–are too busy feasting on the dead bodies.

Still, researchers are very interested in what these tiny picnickers have to say. This grisly lot isn’t some mass murderer’s secret larder; it’s a forensic research facility. It’s here that forensic scientists learn how to determine the time and date of death from a corpse’s remains.

One of the best indicators of how long a body has been dead is the rate of decay, called putrefaction. There are already a host of bacteria inside our bodies, just waiting for us to die. Normally held in check by our living cells, these bacteria start a feeding frenzy as soon as we become a corpse. They reproduce quickly, reducing our soft body tissues to fluid. By measuring how quickly putrefaction occurs under a variety of climate conditions, forensic scientists can help police determine an accurate time of death.

Even after the soft tissue has completely decayed, a forensic scientist can still approximate the date of death from the condition of the bones. Bones that still feel greasy are called “green bones,” and they are relatively fresh. If the body was exposed to the air, a green bone means the corpse is less than a year old. Bones laced with a network of cracks have probably weathered at least one winter.

If your stomach can take more, picture this. A murder has been committed; the scene of the crime is a secluded area. There were no witnesses, and the body is considerably decayed. As the chief investigator, you have a suspect who was in town a week ago. But to convict him, you’ll need to know the date and time that the victim was murdered. How can you tell? And besides, what’s that annoying buzzing in your ear? Wait, don’t swat that fly! He’s your star witness. In fact, that little fly just told you the date of the crime!

Flies don’t carry pocket calendars, and they can’t testify before a jury. How can a crime-scene insect help a police investigation? By doing what it naturally does-eating and laying eggs.

When someone dies outdoors, the first investigators on the scene are usually bright green-bottle blowflies. Attracted by the smell of decaying flesh, these usually arrive within ten minutes of the death. While this smell might make us retch, for the blowfly it’s as savory as grandma’s apple pie. The blowfly’s scientific name is “Sarcophagi,” which means “corpse eater.”

While they eat, the blowflies lay eggs in the softer parts of the body, and these hatch into maggots twenty-four hours later. These maggots attract other insects, like the predatory rove beetle, who feast on them. And so on. Wave after wave of hungry insects arrive, marking time as accurately as a clock.

Meanwhile, the blowflies follow their natural life cycle. Maggots become pupae, the pupae become adults. By surveying the insects in and around a corpse, forensic scientists can help a police investigator determine how long ago a victim was murdered.

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