Corpse-eating tropical fly found in Indiana

8:14 PM, Jul 16, 2013   |    comments
Chrysomya megacephala Fabricius. Photo courtesy of USA TODAY/Courtesy of Indiana University-Purdue University Indianapolis.
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By Shari Rudavsky, The Indianapolis Star

INDIANAPOLIS - Last September, a professor from Indiana University-Purdue University Indianapolis opened a container of rotten chicken meat on campus and waited for the smell of decaying flesh to draw the flies to her.

Did they ever. Among the flies that landed in professor Christine Picard's net was a species that no other forensic entomologist had found this far north.

Not only does the discovery of the blowfly have implications for the way forensic entomologists do their work, it attests to the subtle effects that erratic weather may be having on even the smallest of species.

"That was a significant find," said Neal Haskell, a professor of forensic science at St. Joseph's College of Indiana, a national expert in forensic entomology.

Forensic entomologists such as Picard and Haskell help criminal investigations by studying the insects found on bodies. The number present - and their developmental state - can provide information on how long a person has been dead.

Therefore, knowing the local species and their life cycles is critical.

The fly is known for its large head, as its Latin name - Chrysomya megacephalaFabricius - implies. It is now in the Purdue University Entomological Collections, the lone specimen of its kind. Picard published her find in the July issue of the "Proceedings of the Entomological Society of Washington."

Before Picard's find Sept. 24, the Chrysomya megacephala Fabricius had never been seen farther north than New Mexico. Native to Asia and Africa, the fly was first seen in the southern states of the continental U.S in 1988.

But last summer's hotter-than normal temperatures probably led it to feel comfortable enough to fly north, experts say.

In Rensselaer, Haskell told his students to look for the fly during their weekly collecting trips. But nothing turned up.

"I kind of expected it last year," he said. "It doesn't mean it wasn't here. We just didn't find it. There are not too many people actually looking at blowflies."

Count Picard among the few who are. She studies flies such as this one that breed in and feed on decomposing animal flesh.

"Because these flies will only come to a body after it has passed and they will consume all of the tissue, you can basically work backward," said Picard, an assistant professor of biology in the School of Science at IUPUI.

As a body decomposes, it emits odors that attract these insects. Females lay their eggs in an opening of the body, such as the eyes, nose, mouth or if one exists a gunshot or knife wound. Depending on the species and temperature, the eggs hatch in 24 hours or more.

They hatch as small maggots that go through two additional phases over the next few days. Then they hatch into a third phase in which they are larger and grow more rapidly. Often it's when the flies reach this stage of the life cycle that the body is discovered. At this point, "the body really smells," Picard said.

Throughout these larval stages, the maggots feed on the tissue. When they have reached a certain point in growth, they will leave the body, burrow into some nearby soil or leaves, pupate for a week to a few weeks and emerge as adult flies.

Forensic entomologists look for the oldest insect on the body for an idea of how long it has been dead, Picard said. Often a forensic entomologist may testify at a trial as to how long a body was in a location to support or debunk an alibi.

Because development stages and times differ between species, forensic entomologists need to know not only how to identify flies but also know that individual's life trajectory.

Indiana is typically home to 10 to 12 different species, Picard said.

But in a hot summer like last year's, among the hottest on record, it's not surprising that this species headed north, she and Haskell agreed.

Another tropical blowfly species, the hairy maggot, also in the Chrysomya genus made it north a few years ago borne on the winds from Hurricane Katrina, Haskell said. He saw it for a few years after that and thought it was well-established but this year, he said, he has not seen any specimens.

With Indiana's cool summer this year, no one has seen another specimen of themegacephala species in Indiana.

"If this is a cold summer," said Picard, "it's possible we won't see it."

The Indianapolis Star

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