Black rhinos, an endangered species, are sometimes dehorned to deter poaching.Siphiwe Sibeko / Reuters

They’re often the first arrivals at the scene of the crime—buzzing, sapphire-bodied flies that herald the appearance of other flies, beetles, and a whole buggy ecosystem that will take over a corpse. Known as Chrysomya marginalis, this distinctive, red-eyed blowfly descends upon dead animals to lay eggs, giving their offspring flesh to feast on. And it may be able to help South African authorities catch the poachers who are destroying the country’s rhino population.

In South Africa, poachers kill at least 1,000 rhinos for their horns annually. The horns are sold in East Asian countries such as Vietnam, where they’ve traditionally been used as a remedy for ailments from sexual dysfunction to cancer. No research backs up these purported benefits—the horns are made of the same protein that forms hair and nails—yet poachers continue to target rhinos, particularly in the Kruger National Park, a nature reserve twice the size of Cyprus that straddles South Africa and Mozambique.

Since the poaching explosion in 2008, authorities have tried a number of initiatives to curb the poaching, including the deployment of hundreds of army soldiers to national parks, DNA tracking to follow horns from rhino to market, and drones to surveil large areas of the parks. Still, rangers find the carcasses of these endangered animals, a bloody mess where their horns used to be. So now they’re hoping that one little species of fly could give park rangers and police the data they need to nab poachers.

C. marginalis arrives very promptly at dead things, just after they have died,” says Martin Villet, a professor of entomology at Rhodes University, where he directs the Southern African Forensic Entomology Research Laboratory. The fly has a particular preference for large creatures (usually more than 100 pounds) and lays eggs in a dead body almost immediately.

This timing could make the C. marginalis offspring an ideal marker of how long a corpse has been lying around before it starts visibly decomposing. The insect has four distinct life stages—egg, larva, pupa, and then adult—and the larva sheds its skin twice, allowing for even more specific differentiation. “Very roughly, the egg lasts up to 48 hours, the larva is about five days, and the pupa is about two weeks,” Villet says. “How old the grubs are gives a good estimate as to when [an animal] died.”

The regal bowfly, Chrysomya marginalis
(Wikimedia Commons)

He likens this data to cellphone records, showing where someone was at the time of a crime. “If you know that something has been dead for two days, you know that someone could have travelled for two days,” he says. It narrows down the possible location of the poacher if they are still in the park, or places specific suspects in the vicinity of the crime scene.

“If it’s a very fresh carcass, you may want to increase your efforts in a certain area,” says Danny Govender, a disease ecologist at SANParks, the organization that manages South Africa’s national parks. The data can also aid reporting statistics and monitoring which anti-poaching strategies are working.

Using insects to determine time of death is not new. French veterinarian and entomologist Jean Pierre Mégnin first wrote about the fauna that overrun dead bodies in 1894. More recently, the field of forensic entomology, as it’s called, has begun looking to flies for clues about human deaths, including murders. Forensic entomology could play a big role in the reconsideration of the case of Kirstin Lobato, a woman convicted of murdering a homeless man in Las Vegas in 2001: As reported by The Intercept, the absence of flies or other insects at the crime scene seems to suggest the man was killed hours after Lobato had left the city.

While forensic entomology has been slow to catch on in South Africa, it did briefly rise to prominence in 2000, when a court found, partly based on entomological evidence, that a man had assaulted and murdered a young girl. The 8-year-old’s body was recovered seven weeks after she went missing. Suspicion fell on the neighbor’s son, Albert du Preez Myburgh. But Myburgh had an alibi: He had been in prison at the time of her death, he claimed. Yet one of the flies found on the girl’s body, a species that has a long life cycle, showed that when she was murdered, Myburgh had not in fact been in jail. This was the first time entomological evidence had been used as evidence in a successful conviction.

Despite its promise for deterring poachers, forensic entomology still has some significant hurdles to overcome. Most prominently, there is currently very little data on the actual timeline of the C. marginalis lifecycle, says the South African Police Service’s Melanie Pienaar; experts know roughly when it changes stages, that is, but need to do more studies to gain truly useful information. “Without the data, it is impossible to make an accurate calculation of when the animal was poached,” Pienaar says.

Though insect succession is very useful and can be quite accurate, “there is a fair amount of expertise needed to age a carcass correctly using insects alone,” Govender adds.

For now, the approach is valuable in theory, limited in practice. “There is always room for more research as science, just like insects, just like crime, is constantly evolving and adapting,” the police’s Pienaar says. “The more data available, the more accurate the post-mortem interval estimations can be done.”

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