Fly witness.

Detectives know that clues to a crime can literally fly away.

In a recent criminal case, flies helped nab the crooks. Here's what happened: Two baby black bears were found shot to death near Winnipeg, Canada, in July 1995. Their tiny gallbladders had been removed, most likely to be sold as medicine in Asia. The suspects? Two men hiding nearby. Witnesses who heard gunshots had spotted their vehicle. Police arrested the suspects but needed indisputable evidence to convict them of poaching, or illegal hunting.

The evidence? Insects crawling on the cubs' carcasses. A police officer found and collected blowfly eggs from the body of one cub and wrote down the time when the eggs hatched. He then packed the larvae with pieces of bear liver (for food), and sent them to an entomologist, or insect scientist, in British Columbia, Canada.

The scientist, Gail Anderson, knew that blowflies invade a body and lay their eggs on it within minutes after death. She also knew that the eggs of this species of blowfly take about 22 hours to hatch in hot summer temperatures. So Anderson counted back 22 hours from the time the eggs hatched to find out when they were laid--and consequently when the cubs were killed. That time coincided with the time witnesses said they had heard the gunshots and saw the suspects in the area.

Last March, the poachers were sentenced to jail for six months. It was the first time that forensic entomology, the science of using insects to solve crimes, helped secure a poaching conviction in Canada.

CLUES `R' BUGS

In recent years, insects have earned the respect of criminal investigators. Bugs have helped police build cases against drug traffickers, since insects found on contraband can be traced to the source country. More often, insects are useful in murder cases--both animal and human--because they help pin the time of death so accurately.

Bugs were probably first used to track down a killer in 13th-century China. A person had been slashed to death in a village. The investigator gathered all the men and told them to lay out their sickles in the sun. Flies came swarming to one, most likely attracted to the smell of blood. The owner confessed to the crime.

Nowadays, murder investigators carefully collect insect eggs and maggots from a dead body and sweep the air with fine-mesh nets to bring in bug witnesses. Police keep some of the bugs alive and put the rest in alcohol to preserve them. Then they send the bugs to one of the 20 forensic entomologists in the United States. Using these bugs, scientists can find clues about a death.

INVASION OF THE BLOWFLIES

When a person or animal dies, cells in the body immediately begin to break down and give off a subtle odor. Blowflies use their keen sense of smell to zero in on the corpse within minutes.

Blowflies, like many insects, go through stages of their life cycle--egg to larva to pupa to adult--with incredible precision (see blowfly life cycle, p. 9). After determining a bug's age, entomologists can count the hours or days back to the time of death, as Anderson did. Entomologists also take into account weather conditions and temperature around the time a body is found. That's because rain may delay bugs coming to the scene. And high temperatures make eggs hatch faster and larvae grow more quickly than normal.

Together, these variables could tie a suspect to the murder--or even establish his or her innocence.

BUGGING OUT!

While blowflies are the first insects to visit a dead body, other bugs soon follow. After blowflies come flesh flies, which give birth to live larvae. "When the larvae start developing and feeding on the corpse, they get into these masses that can clean tissue by the hour," says Richard Merritt, an entomologist at Michigan State University. "They're just a feeding machine."

A day or two later, beetles and wasps come to feed on the fly eggs and larvae. Carrion beetles soon follow to devour rotting flesh. After a month, creepy crawlies like mites and skin beetles arrive to get their share of dried skin and hair.

This predictable succession of insects also helps scientists determine time of death. But there are limits to forensic entomology. "The longer a body has been expose outside, the harder it is to use insects," Merritt explains. "Once you get past a month or two, it becomes harder to associate insects with the time of death." By then, insects found near a body could be second-generation. If investigators don't realize they're dealing with second-generation scavengers, they could draw the wrong conclusions.

LITTLE HELPERS

Bugs can also help determine if a body has been moved from the scene of the crime. Different species have different habitat preferences--they live and grow in specific places. For example, one species of green bottle fly prefers well-lit areas, while a species of black blowfly likes shade.

When investigators found black blowflies on the rotting body of a woman in a Maryland landfill, they became suspicious. Her remains, discovered in July 1984, lay in an area often exposed to direct sunlight and frequented by green bottle flies. Since no green bottle flies were found on her body, investigators concluded that she had been moved from a more shaded environment preferred by black blowflies. Police used this and other evidence to track down the killer--a truck driver who had hidden the body in his trailer for several days.

Sometimes bugs can provide clues to the cause of death. Drugs or poison, which affect insects' life cycles, can be traced in larvae.

Forensic entomologists tested maggots found on the body of a young man discovered in a wooded area in Connecticut in February 1990. Police found no stab wounds or bullet holes on the corpse. But scientists found traces of cocaine in the maggots. Further investigation revealed that the man had a history of drug use. Police ruled his death an overdose.

Entomologists also take blood samples from some insects. Cockroaches and bedbugs found at a crime scene, for example, sometimes retain human blood, which could belong to the victim or even the murderer. "If you find a blood type that is different than the victim's, it could mean that someone else was shot and fled the scene," explains entomologist Louis Sorkin of the American Museum of Natural History in New York City.

In fact, bugs provide so many clues to crimes, they're becoming an invaluable tool for investigators. "I think police officers are realizing the importance of insects," says Merritt. "Ten years ago, they'd just have said, `Get out of here!'"

RELATED ARTICLE: Blowfly Life Cycle

1. A blowfly can smell rotting flesh from up to a mile away. The female fly zooms in and lays 200 to 500 eggs on the body.

2. Blowfly eggs measure about 2 mm in length. In summer temperatures, the eggs take less than one day to hatch.

3. Newly-hatched larvae measure about 5 mm long. They feed on a corpse for 8 to 12 days, then crawl away to look for a dry place.

4. During the pupa stage, the larvae's outer body covering hardens and darkens with age. After 18 to 24 days, adult blowflies emerge.

RELATED ARTICLE: Insect Inspector

For entomologist Gail Anderson, a warm, sunny day is perfect for doing research. That's when flies like to swarm around dead pigs, laying eggs on the carcasses. Anderson and her students then observe which bugs come to the bodies and when.

As the first (and currently only) full-time forensic entomologist in Canada, Anderson assists in about 20 murder cases a year, determining time of death based on bugs found on a corpse.

Anderson became a forensic entomologist "accidentally," she says. While studying entomology in college, an advisor asked if she would be interested in forensics (crime science). She decided to try it, and found that she enjoyed the work. "I like to do something useful," she explains. Thanks to Anderson's expertise, Canadian police now have a reliable way of estimating when a person died.

Do maggots crawling out of rotting bodies gross her out? "I'm a biologist," says Anderson. "I don't find anything gross. I've seen worse in PG-rated movies."

To find out about a career in forensic entomology, write: American Board of Forensic Entomology c/o Dept. of Entomology Univ. of Hawaii at Manoa 3050 Maile Way Honolulu, HI 96822 or e-mail: [e-mail]