“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.”

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.