The Why Files The Why Files --

CSI: Crime Seen, Investigated

POSTED 14 JULY 2005 (Originally posted 1996)
Most peculiar dating game
If you die without being buried or cremated, you rejoin the wheel of life, the cycle of eat-or-be-eaten we dignify by the august term "nature." In particular, if your body lies above ground:

You emit an appetizing stink (to flies that lay eggs on dead people).

You are too preoccupied with being dead to bother swatting those flies.

Small, iridescent green fly with large eyesThose flies lay their eggs on you.

The hairy blowfly is a common visitor to corpses down under. Photo: Dept. of Agriculture of Western Australia

Flies are so good at finding corpses that they may arrive within an hour of death -- before you're even cold. Carrion flies accomplish this miracle of mortuo-location by scenting putrescine and cadaverine, two quaintly named exudates of cadavers.

It's the wheel of life: Flies flourish while bodies decomposeWithin days, those eggs hatch into maggots that will grow through several larval stages into pupae until they finally become old-enough-to-drink-and-vote insects.

The forensic angle is kinda disgusting -- we did warn you -- but the developmental stage of your flies does suggest when you died. The trick is to work backwards: Find the most mature form of the insect and figure out when its eggs could have been laid. Since flies usually wait until after death to lay eggs, the victim must have already died at that point.

The eggs of forensic entomology were laid in the 1880s, when insect-infested bodies were found in mass graves in Germany and France. Investigators realized they could date the deaths if they understood the development of those flesh-eating flies (see "A Brief History..." in the bibliography).

Flies in the face of reality
Answering questions about development rate has made the field of forensic entomology a force in murder investigations. Forensic entomology -- call it CSI-Fly? -- concentrates on how fast various flies develop in various conditions. Since higher temperatures produce faster chemical reactions, temperature rules in these investigations. But establishing the average temperature of a corpse can be a bother. "It's not too often that a person dies under a weather station, but it happens," Bullington observed during a 1996 conversation with The Why Files.

Winged insect with black and white patterned backCrime investigators collect this Sarcophagidae fly from corpses in Australia. Photo: Dept. of Agriculture of Western Australia

With weather stations usually miles away, an investigator must estimate ambient temperature. Then, relying on laboratory studies of fly development, the entomologist will produce a range of possible times of death. "There's a lot of margin for error," Bullington said.

But you can hit the jackpot, as Bullington found in a 1994 triple-murder in Allentown, Pennsylvania. The killer had considerately cranked up the air-conditioning and stuffed towels under the door of the murder scene. Although Bullington knew the precise temperature, he still could not pinpoint the time of death, since the fly he found had a variable hatching rate. Nonetheless, the three-day range he calculated helped pin the crime on the father in the family. (The suspect didn't testify. He didn't even hatch a decent alibi, since he'd meanwhile shot himself to death in Colorado.)

Entry of entomological innovation
The practice of fly-dating corpses is now spreading around the world. In 2001, Thai scientists used insects to conclude that a mummified corpse had lain in the forest for three to six months. In 2000, in an effort to push CSI-Fly south of the Equator, Brazilian entomologists inventoried interesting insects on dead pigs and humans. The researchers observed that life on a rotting carcass passes through "a process of ecological succession. Therefore, the insects arrive in a determined sequence, producing an addition and/or substitution of species." (see "A Checklist ..." in the bibliography).

So it's not just buff, determined young scientists -- but also the principles of ecology -- that are helping in crime scene investigations...

Maggot milkshake
Beyond the all-important "date-of-death" question, forensic entomologists may also reveal where a suspect has traveled -- if insect larvae appear on muddy boots or vehicles.

Oval eggs rest in brown, stringy messCollect 'em all! Maggots can help date a corpse.
Photo: Dept. of Agriculture of Western Australia

Flies might also answer an embarrassing question after you are gone: What drugs were ya taking? You might hope to take evidence of your personal failings to the grave, but what if it could implicate the bad guy? Help is on the way from Virginia Commonwealth University, where scientists are working on, what else, the "maggot milkshake."

The principle is simple, VCU toxicology graduate student Michelle Peace wrote in 2002. "You are what you eat. So if the body had taken any type of drugs prior to death, and the maggots are eating on that body, then the drugs are going to wind up in the maggots."


Here's the scoop. In a hot, humid climate, a writhing mess of maggots can quickly reduce you to a heap of bones. But if you could find a way to analyze toxins from the maggots, you would produce a voice from beyond the grave. To make a maggot milkshake, you cram maggots direct from the corpse in the ol' Waring blender, and off you go. If the victim had taken drugs -- or perhaps been poisoned -- you might develop leads for a murder investigation.

Lords of the flies?
The field of forensic entomology is like that -- unpalatable science put to good use -- but it has a good reputation, says Kobilinsky of John Jay College. "I only know a few forensic entomologists, but those that I know are true professionals. They are generally university types, they have been studying entomology for years, they understand the succession in the life cycle of these insects." When entomologists offer contradictory testimony on time of death, he says, that "may very well be an honest different of opinion."

fly and bloodThese green-bottle flies in the family Calliphoridae are common carrion flies. About the size of a large house fly, they like the sun. Faster than you can pronounce "putrescine," this fly can reach most large, sunlit corpses within minutes of death. (Putrescine and cadaverine are two "putri-fumes" made by dead people.) Photo: Courtesy Stephen Bullington

But Jason Byrd, a forensic entomologist in the Department of Criminology, Law and Society at the University of Florida (Gainesville), emailed us with a different take. "I'm not sure if anyone has been 'railroaded' based on testimony of a forensic entomologist. But I can tell you that inaccurate information is put forth before the jury, judge, and attorney in many, many, cases. Unfortunately the opposing attorney rarely does the homework needed to properly counter such testimony. Usually, the opposing attorney simply questions the is indeed very rare for them to go so far as to call in an 'opposing' entomologist."

What can forensic science tell about words on paper?


Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

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