Detectives look to insects for clues to crack cases

Flies that wiggle in dead bodies can give forensic scientists clues to pinpoint time of death. Photo courtesy: Fir0002/Flagstaffotos

A lot of dead bodies turn up on Mount Hamilton and in the Santa Cruz Mountains, two natural areas near San Jose, Calif. Some bodies are found decomposed beyond recognition. Jeffrey Honda has worked on a number of these cases. He searches for subtle clues that might help find a killer or put a name to a victim. But Honda isn’t a police officer. He’s an entomologist.

Insects and death have a tight relationship: these tiny creatures help dead things decompose. “If there’s a body out there, they will find it because they can smell decay from a mile away,” said Honda, who teaches a course in forensic entomology at San Jose State University. Those who follow the traces of insects may see a story that other detectives miss.

A blowfly – usually the first insect to land on a corpse – can search up to  12 miles each day looking for death and decay. The female fly scurries over a body searching for suitable spot of moist flesh. There, she’ll lay batches of eggs – the shape of grains of rice – by the hundreds.

Within a day, the eggs hatch into maggots – white, wormlike larvae. The larvae bite and chew their way below the surface. As the maggots feast, they grow and develop, turning from first instar to second, and third.

A young fly’s measured growth – like steps on a ladder – provide a timeline for death. Honda looks at the tiny larvae under the microscope and pinpoints how long a body has been exposed. “The bugs don’t lie,” said Honda. “They have to develop in a stereotypical fashion.”

The life cycle of a housefly. Credit: HowStuffWorks.com

During one investigation, detectives handed him a sample of insects from an infant found dead in Palo Alto, according to Honda. Officers couldn’t pinpoint the time of death. The small body was badly decomposed, suggesting it died a long time ago.  Even though the remains were found outside, “it was missing a whole suite of flies you’d expect to see on a body that was out for that amount of time,” said Honda.

For a body with such extensive decay, Honda though it must have been stashed inside, protected from insects. This was the clue that detectives needed and the suspect confessed.

Flies can also tell entomologists if a body was moved, like when scientists find city flies in bodies discovered in the country.

In Santa Clara County, Honda and his students have lured flies to traps baited with chunks of liver. By sifting through thousands of dead flies, the team has been able to determine which flies are more active at different times of the year, creating a forensic calendar.

But insects can often trick forensic scientists and law enforcement that isn’t bug savvy, said Honda.

When maggots finish feeding they meander from their meal to pupate. The flies enclose themselves in a stiff, dark shell and begin to metamorphose into their adult, flying form. But these dark pellets can be deceiving.

“To the untrained eye, they actually look like rat droppings,” said Honda, who provided a list of other insect mix-ups.

For instance, in an enclosed area, adult flies can gorge themselves on blood from a dead body. Plump with blood, these overstuffed flies vomit and defecate blood, leaving blotchy areas around a room. The blotches look like blood splatter.

Roaches and ants can also gnaw and chew on dead skin. These insects leave marks, which – to investigators – can look like acid burns.

Credit: By Yumi Kimura, via Wikimedia Commons

Honda trains students to know what to look for at a crime scene. But insects can help discover invisible clues as well.

Some forensic scientists use insects to figure out what drugs were in a person’s system when they died. If blood or other tissues are not available, insects can be tested for the presence drugs like cocaine, heroin, and methamphetamines.

Insect evidence alone can’t replace traditional forensics, said Honda. “I like to think of it as another tool in the toolbox to augment what’s already there.”