It’s often said that we live in a dog-eat-dog world. And it’s not just dogs—cannibalism is widespread in the animal kingdom. But snakes are usually considered an exception to this rule—a group of species that rarely eats their own, except during times of extreme hardship.
That paradigm seems to be collapsing, though, as study after study finds evidence for cannibalism in snakes. In a new paper, researchers report that some of the most notorious snakes on Earth—cobras—regularly consume their own kind.
When herpetologist Bryan Maritz heard the radio call saying there were “two large yellow snakes fighting,” he rushed into action. Maritz, a researcher with the University of Western Cape in South Africa, was in the Kalahari Desert in search of Cape cobras (Naja nivea) and boomslangs (Dispholidus typus) for his ongoing research into their resource use.
When he and his colleagues found the snakes 15 minutes later, the larger one was in the process of downing its smaller rival. “Instead of capturing two potential study animals, we found one well-fed study animal,” Maritz and his colleagues explained in their paper published this week in the journal Ecology. The snake was outfitted with a radio transmitter and nicknamed Hannibal.
Cape cobras are generalist predators that have no qualms eating other snakes, including already-dead ones. Indeed, many snake species will hunt other snakes opportunistically, and some — like the infamous king cobra (Ophiophagus hannah) — have made serpents the majority of their diet. But for the most part, it’s believed that these snakes prey upon other species, not their own. So seeing this supposedly uncommon event made Maritz wonder if the practice wasn’t so rare after all.
He and his colleagues combed through the scientific literature looking for reports of snake-eating — what scientists refer to as ophiophagy — in the six species of cobra that live in southern Africa. They also mined reports made by local citizen scientists in a public Facebook group.
“We knew they ate snakes,” says Maritz. “What we didn’t know was that snakes form a huge part of their diet.” Between 14 and 43 percent of each species’ diet consisted of snakes, they found. The cobras are apparently especially fond of puff adders (Bitis arietans); the African viper accounted for almost a third of the snake prey recorded.
More surprisingly, five of the six species were seen eating their own kind. Cape cobras were particularly cannibalistic, as members of their own species comprised 4 percent of the feeding observations tallied in this study. That stood out, given that an extensive review conducted 11 years earlier found no evidence for cannibalism in the species.
What was really weird was that every cannibalism event Maritz and his colleagues found in Cape cobras was a male eating another male. That suggests the practice might have come secondary to fights over resources or mating.
“The potential link between male-male combat and cannibalism is tantalizing,” Maritz says. Admittedly, the dataset is small, so it’s possible that females commit cannibalism, too. They just didn’t find any cases of it.
The male exclusivity also intrigues William Hayes, a snake expert and behavioral ecologist with Loma Linda University in California, who says he found the study “fascinating.”
“We might be tempted to assume that the effects of ophiophagy in this group are minor, but relatively rare events can sometimes have profound implications,” he says. “Eating a single competitor might, indeed, mean the difference between survival or securing a mating.”
It’s not necessarily surprising, though, that these snakes would take the opportunity to consume a smaller snake they stumble across or even defeat in battle, says Kate Jackson, a herpetologist with Whitman College in Washington who was not involved in the study. If you’re long and skinny, the biggest meal that fits in your mouth is something else long and skinny, she notes.
Jackson — who has studied the mechanics of snake-on-snake predation in kingsnakes — says she was “delighted” to see this kind of work being conducted. “Too much of what is known of the diets of snakes in the wild is based only on lists of prey items obtained from field guides,” and not novel research, she says.
Jackson notes the study is especially important because of the impacts cobras have on people. Cobras are among the most dangerous snakes in Africa because of their potent venoms. But the proportions and even types of toxins in those venoms may vary based on what the snakes eat, so if the diets of these species vary in different areas, the snakes themselves could have different venoms—and that could mean an anti-venom that saves lives in one region is less effective in another.
The paper suggests that snake cannibalism could play a large role in structuring snake communities—determining the type and size of snakes found in a certain area. This might be seen on a smaller scale in his study area, where large cobras are known to raid the large, colonial nests of weaver birds. “Visiting those nests might be dangerous for smaller cobras if the nests are also attracting bigger cobras—potential cannibals,” he says.