How Hannibal the cannibal led to a discovery about cobra diet | Science News for Students

How Hannibal the cannibal led to a discovery about cobra diet

A sighting of one cape cobra eating another sparked a study of cannibalism
Oct 25, 2018 — 6:45 am EST
cobra cannibalizing another cobra

Scientists working in the Kalahari Desert spotted this cape cobra, which they later named Hannibal, eating a smaller cape cobra. That set off a search for how common the practice of cobra cannibalism really is.

Courtesy of B. Maritz

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

Bryan Maritz is a herpetologist, or reptile biologist. He works at the University of the Western Cape, in Bellville, South Africa. He hadn’t set out to study cobra cannibalism. His team had been conducting a study in the Kalahari Desert. They were looking at two species of snakes: cape cobras and boomslang. Social weavers are birds. “The snakes raid these huge colonial social weaver nests and eat all the chicks and eggs,” Maritz notes. The researchers wanted to understand better how the two species use the bird nests. As part of their study, they were looking for snakes that they could implant with radio transmitters.

One day this past January, while searching for snakes, the researchers got a radio call. A tour guide 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 over. They didn’t find a snake fight. One large cape cobra was swallowing a smaller one. “Instead of capturing two potential study animals, we found one well-fed study animal, now known as NN011,” Maritz and his colleagues write in a paper published October 1 in Ecology. They nicknamed the snake Hannibal.

This wasn’t the first documented sighting of a cannibal cobra. However, scientists had never thought such behavior was common. “The total number of observations of cobras eating in the wild isn’t a big number,” Maritz says. “And the observations of cannibalism in the wild are even rarer. So I think it’s easy to dismiss as a one-off thing.”

But Maritz had an inkling this practice might not be so rare. Before starting the cape cobra-boomslang study, he’d had students dissect museum specimens. 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 scoured reports of cobra diets in research papers, newsletters and museum bulletins. They also solicited stories on Facebook. Some 30 species of cobras live in Africa and Asia. The team, though, restricted their analysis to six species, including the cape cobra of southern Africa.

Snake-eating, they found, was common among five of the six species studied. Other snakes accounted for 13 percent to 43 percent of the cobras’ diets. Snakes eating members of their own species represented about 4 percent of all prey in the study. All cobra species eat similar things. So the scientists now think cannibalism might be a trait shared by even more types of cobras.

In all the cannibalism events that the researchers witnessed, both the eater and the eaten were males. That leads them to suspect that this behavior may be a guy thing. More research is needed to confirm that. 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?”

Power Words

(for more about Power Words, click here)

behavior     The way something, often a person or other organism, acts towards others, or conducts itself.

colleague     Someone who works with another; a co-worker or team member.

dissect     (in biology) To open up animals or plants to view their anatomy.

ecology      A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

herpetology     The biology of reptiles and amphibians. Scientists who work in this field are known as herpetologists.

implant     A device manufactured to replace a missing biological structure, to support a damaged biological structure, or to enhance an existing biological structure. Examples include artificial hips, knees and teeth; pacemakers; and the insulin pumps used to treat diabetes. Or some device installed surgically into an animal’s body to collect information on the individual (such as its temperature, blood pressure or activity cycle).

prey     (n.) Animal species eaten by others. (v.) To attack and eat another species.

radio     To send and receive radio waves, or the device that receives these transmissions.

social     (adj.) Relating to gatherings of people; a term for animals (or people) that prefer to exist in groups. (noun) A gathering of people, for instance those who belong to a club or other organization, for the purpose of enjoying each other’s company.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

trait     A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.

Citation

Journal:​ B. Maritz et al. The underappreciated extent of cannibalism and ophiophagy in African cobras. Ecology. Published online October 1, 2018. doi: 10.1002/ecy.2522.

Journal: I. Layloo et al. Diet and feeding in the Cape Cobra, Naja nivea. African Journal of Herpetology. Published online December 15, 2017. doi: 10.1080/21564574.2017.1388297.