How a snake named Hannibal led to a discovery about cobra cannibalism

Studying the diet of snakes isn’t easy. The animals are elusive, and they don’t feed all that often. It probably doesn’t help that some of them can be deadly to humans. So perhaps it’s not much of a surprise that scientists hadn’t realized how common one category of snack is for southern African cobras: each other. But once researchers started looking, they realized that cannibalism among cobras happens far more frequently than anyone had thought.

Bryan Maritz, a herpetologist at the University of the Western Cape in Bellville, South Africa, hadn’t set out to study cobra cannibalism. He and his colleagues were conducting a study in the Kalahari Desert of two species of snakes: cape cobras and boomslang.

“The snakes raid these huge colonial social weaver nests and eat all the chicks and eggs,” Maritz says. The researchers want to better understand how the two species use the birds and their nests, and they were looking for snakes that they could implant with radio transmitters.

One day this past January, though, while searching for snakes, the researchers got a radio call from a tour guide who told them where to find a pair of large yellow snakes engaged in a fight. Thinking those yellow snakes might be cape cobras, the team raced to the site. They didn’t find a snake fight but did find one large cape cobra swallowing a smaller one.

“Instead of capturing two potential study animals, we found one well-fed study animal, now known as NN011, or more casually, Hannibal,” Maritz and his colleagues write in a paper published October 1 in Ecology.

This wasn’t the first documented sighting of a cannibalistic cobra, but scientists didn’t think such behavior was common. “The total number of observations of cobras eating in the wild isn’t a big number, and the observations of cannibalism in the wild are even rarer, so I think it’s easy to dismiss as a one-off thing,” Maritz says.

But Maritz had previous inklings that this practice might not be so rare. Before starting the cape cobra-boomslang study, he’d had students dissect museum specimens, and they found a surprising number of cape cobras that had eaten other cape cobras. The discovery of Hannibal, though, persuaded him that he needed to investigate just how common the practice was.

Maritz and his colleagues went looking for reports of cobra diets in research papers, newsletters and museum bulletins, and also solicited stories on Facebook. There are some 30 species of cobras in Africa and Asia, but the team restricted their analysis to six species, including the cape cobra, in southern Africa.

Snake-eating, they found, was common among five of the six species studied, accounting for 13 to 43 percent of the cobras’ diets. Conspecifics, snakes of the same species, represented about 4 percent of all prey items in the study, the researchers found. And because all cobra species share similar diets, the scientists think that cannibalism might be a characteristic shared by even more cobra species.

In all the cannibalism events that the researchers witnessed themselves, both the eater and the eaten were males, leading them to suspect that this behavior may be a male-only trait. More research will be needed to determine if that’s true. But if it is, Maritz says, “I could see it playing a role in competition for resources or mates. What better way to get ahead in life [than to] eat the guy who is taking your food and mating with females that you might want to mate with?”