The first murder solved with the help of insects, per an account written in the year 1235, took place in China. A villager was found slashed to death. The judge summoned local farmers and told them to bring their sickles. As the farmers stood in the summer heat, insects swarmed around one man's tool — drawn to traces of blood left on the blade. The man confessed. The telltale bugs, Hawaiian forensic entomologist M. Lee Goff wrote in his 2000 book, “A Fly for the Prosecution,” were “certainly blow flies.”
Seven centuries later, investigators still look to blow flies, maggots and other insects for evidence. Bodies are ripe “to be colonized by plants and animals,” Goff wrote, like volcanic islands freshly erupted from the sea. Some bugs can smell a decomposing body from miles away. They come to feed. Or they'll lay eggs in the nose, eyes and throat. Based on who's still eating or whose eggs have hatched when the victim is discovered, experts can sketch a rough history of the corpse.
But there are limits to what scientists can divine from insects. Bug behavior rarely provides precise timelines. In particular, “numerous weaknesses and erroneous beliefs” plague the use of insects to reveal whether a body has been moved, according to the authors of a report published Tuesday in the journal PeerJ.
Damien Charabidze, a forensic entomologist at the University of Lille in France, reviewed more than 170 scientific articles and case reports about bugs and corpse relocation. He found that, although TV shows and textbooks imply that bugs can act as a corpse's six-legged return address, this rarely bears out in practice.
“Only a few forensic cases have actually been solved using such a method,” he said. Those that were required “good timing, an accurate sampling, a little bit of luck” as well as “a huge background knowledge” in local biology.
There were a few cases that drew headlines: In 1991, the presence of urban bugs on a corpse tipped off investigators that the victim, found in the Palm Springs, Calif., desert, had been killed in a city warehouse. In 2007, two bodies uncovered in a forested Italian mountain were revealed to have been killed separately. One body housed flies called Chrysomya albiceps, which Charabidze said was an “unusual” species; it lives in central and northern Europe only for a few weeks in hot summers. The body, the investigators concluded, must have been killed at lower altitudes and taken up the mountain.
(As for non-murderous crimes, not studied in the PeerJ review, insect experts once traced the origin of marijuana smuggled into New Zealand by looking at the beetles among the plants.)
It's relatively easy to detect when corpses were moved from water to open air, as long as the animals — like aquatic midges or snails — remain on the body. Jeffrey D. Wells, an entomologist at Florida International University who was not involved with this report, said there is also a big difference between buried corpses and those left in the open.
Tiny insects called scuttle flies are “very good at crawling into tight spaces,” he said, such as buried bodies or those wrapped in plastic and put in the trunk of a car. But you'll hardly ever find them on exposed bodies. Unless the corpse was moved. “It's not a ridiculous scenario. Bodies do get buried and dug up again,” Wells said.
Otherwise, though, shifts may be difficult to detect, such as from an urban surface to a rural one, or a body that was buried for a few weeks and then moved indoors. “To suggest relocation, it is necessary to sample on the corpse something that should not be there,” Charabidze said. That's easier said than done. Time is one factor. The cadaver must remain in the first spot long enough to attract bugs. But it can't stay too long in the second place, or the initial colonizers might scurry away.
Investigators also have to be sure that the insects must live in separate regions, he said. And the domain of some corpse bugs is large. A hairy bluebottle fly named Cynomya mortuorum, for instance, can be found hunting for carrion across northern Europe and Asia.
“Experiments should always be performed to check if something that appears 'unusual' really is,” he said, encouraging entomologists to trap insects where the body is found as well as where the corpse might have come from.
Looking at scientific records alone, Charabidze found a potential sticking point: Maps of many corpse-eating bug populations are spotty. (Somehow, such bugs are “infrequently sought out and are poorly known among entomologists,” Charabidze and his colleagues wrote.)
Generating such data isn't easy. “Once you start doing experiments on whole cadavers that’s a huge amount of work,” Wells said. “That’s really labor intensive, even using an animal carcass.” A midsize dead animal might attract hundreds of thousands of bugs, he said.
Charabidze said that the future of forensic entomology will be cases beyond those requiring simply a place or time of death. “A mobile phone can give you an accurate idea of victim's location and date,” he said. Genetics, he said, such as looking for a victim's DNA in a maggot's guts, “will take on more and more importance in the next years.”