Panorpa nuptialis is feeding on scalp fluids from autopsy incisions. (Entomological Society of America)

Like so many cop shows, some scenes in the hit television series CSI are devoted to a lowly maggot. This doesn't always describe the criminal suspect. It also describes a helpful friend, the common blowfly and its larvae.

Blowflies are thought to be the first on the scene of a homicide, and sometimes play a starring role as forensic investigators examine DNA in their guts and larvae they leave at the scene for clues to solve murders. So when a researcher at Sam Houston State University in Huntsville, Tex., got a rare opportunity to conduct forensic field tests using a human corpse, rather than animals such as pigs that are normally used, she expected see tons of blowflies.

What actually happened could change the things forensic sleuths look for in human remains while trying to solve how they met their end, according to a new study released Thursday. The first animal on the scene wasn't a blowfly. It was the big, bad scorpion fly with a curling and intimidating tail, a predator of bugs thought to be harmless to humans. Not only did scorpion flies feed greedily on the cadaver, they performed mating dances and copulated in between.

Scorpion flies that buzz gardens and the edge of woodlands were known to gravitate only to animal carrion, said the researcher, Natalie K. Lindgren, a student at Sam Houston who was the study's lead author. "The interesting thing about scorpion flies on human cadavers is they showed up first and remained there for a while." Lindgren said this was a big deal because "we already know who we expect to see first," but the never before documented presence of scorpion flies on a human body left on soft dirt in a sub-tropical bog in Hunstville is "expanding our understanding of decomposition ecology."

Blowflies eventually showed up with their shiny blue and green coats, along with the screwworm fly, but they were smaller in number than the larger and more muscular scorpion fly. Lindgren paused to point out, for the record, that the scorpion fly "is really not a fly at all; it's from an order completely separate from flies," in spite of its name.

When Lindgren saw it in the field, she said she didn't know she was seeing something rare. It wasn't until she went back to the university and delved into previous research that she realized she had made a discovery. Most human bodies are dug up by archaeologists, not entomologists, so those researchers could have seen scorpion flies in action long before now without giving a second thought to the significance.

The president-elect of the North American Forensic Entomology Association, Jason H. Byrd, said the findings of the study are indeed significant.  "Entomologists rely on insect succession to help them determine portions of the postmortem interval, and having a study that indicates that (scorpion flies) are early-arriving species will certainly assist forensic entomologists in their investigations."

Byrd said he wouldn't call the finding "a major breakthrough," but "a small part of the overall puzzle" that help forensic pathologists in their difficult task of learning exactly what killed people. Knowing the scorpion fly plays a role, particularly in fall months when it's active, can help scientists more accurately determine time a death.

Lindgren caught a break on her way to making this finding. "I was in the right place at the right time," she said. The Southeast Texas Applied Forensic Science facility located in the Center for Biological Field Studies at Sam Houston State happened to have cadavers she could use for a yearlong experiment.

Her test subject was a 76-year-old man who died of natural causes in January 2009. His body was kept in coolers 111 days before it was placed outdoors in a remote area with partially filtered sunlight for the study five months after death. He was laid face down on soil near a small stream and left there until late September as researchers checked his remains four to five times per day, Lindgren said, collecting insects each time.

"I had no thought of turning down an opportunity to work on cadavers," something she had never done. Her previous work was with pigs, used to simulate humans because they're hairless with a somewhat similar body fat. "We don’t have enough decomposition research facilities. There were only four or five using human. Anybody can use animals."

Working with humans can get emotional, Lindgren said, but "once you realize that person or family wanted the body used for research, you feel kind of good about what you’re doing, trying to discover things and making science stronger."


Noctuid caterpillar feeds on dried skin near the toenails of a cadaver. (Entomological Society of America)