Snakes keep evolving into cannibals — here's what scientists think is going on

Cannibalism might seem like a rare and unnatural occurrence, but the behavior has arisen in several snake lineages throughout evolutionary history, often triggered by environmental stressors, scientists theorize.

When researchers reviewed 500 reports of cannibalistic behavior across snake species, they found that cannibalism has evolved independently at least 11 times, according to a study published Nov. 2, 2025, in the journal Biological Reviews.

These cannibalistic behaviors occur in diverse contexts, but overall, cannibalism is common and seems to emerge repeatedly because it's beneficial to snakes in situations where they need to make opportunistic dietary choices, the researchers suggest.

"For us humans, we don't think of cannibalism as something common –– it's something weird and disgusting," Bruna Falcão, lead author of the study and a graduate student in biology at the University of São Paulo, told Live Science. "But for snakes, it's good for them; it's good for their ecological fitness. … It's strategic."

Evolutionary advantages of cannibalism

Some of the best-known examples of cannibalism in nature are seen in spiders and praying mantises during mating, as it may be beneficial for females to eat their mates. "Cannibalism is widespread throughout the animal kingdom," Xavier Glaudas, a biologist and National Geographic Explorer who was not involved with the study, told Live Science.

Although scientists previously considered the behavior maladaptive –– meaning it's not beneficial for a species overall –– more and more studies reporting cannibalism in animals hypothesize reasons for the evolution of the behavior. For example, it could help parents control brood size, or it might arise as a response to limited resource availability, a form of population control, or an opportunistic predation choice.

Cannibalistic behavior in snakes has typically been recounted in brief and isolated reports, Glaudas said. For example, his research team described male Montpellier snakes (Malpolon monspessulanus) feeding on female snakes in France — a behavior thought to be driven by limited food resources, especially during times of scarcity outside the mating season. (It would be considered unusual for males to eat females during the mating season, as this would reduce mating opportunities.)

In addition to being widespread in snakes, cannibalism has evolved independently across different snake lineages and regions, according to the study, which combined numerous reports to explain the behavior.

The research team gathered 503 cases of reported cannibalism across 207 snake species. The reports spanned a wide range of snake groups, as well as all continents where snakes live, including reports of snakes both in the wild and in captivity.

"None of us expected that … snakes could be so cannibalistic, and no one was talking about it," Falcão said. "The more we were searching, the more cases we found."

Cannibalism was most common in the Colubridae, Viperidae and Elapidae families, the team found. Colubridae is the biggest family of snakes and made up 29% of all reports. Because this family is not typically known to prey on snakes, however, the authors proposed that most cases of cannibalism in this group may be connected to stressors such as a lack of other food sources. Members of the Viperidae family, which includes vipers, made up 21% of all cannibalism reports. But these were mostly cases in captivity, the researchers noted, so captivity-related stressors, like confinement to small spaces with limited food, may have resulted in cannibalism.

Elapidae, the snake family that includes cobras, accounted for about 19% of the cannibalism reports. This wasn't very surprising, the researchers said, because cobras are known to prey on other snakes in the wild.

Almost half of the cannibal snake species have generalist diets, according to the study, and the researchers linked this dietary flexibility to cannibalistic behavior when necessary. However, Glaudas suggested this connection may not be clear, since the researchers defined only 47.7% of the cannibal snake species as generalist; evidence for the relationship would be stronger if the percentage were higher, he said.

"In regard to the idea that cannibalism could be more common in generalist species, I am a bit more skeptical about the data presented," Glaudas said.

Cannibalistic behavior does seem to be correlated with jaw structure, so whether a snake has jaws that can open wide enough to consume another snake is a key factor; there were no reports of cannibalism in snake species without this ability.

When the researchers analyzed cannibalistic behavior across snakes' evolutionary history, they concluded that the behavior evolved independently at least 11 times throughout the snake evolutionary tree.

Because most reports of cannibalism in snakes are anecdotal, Glaudas said, the study provides a useful overview. This is a "welcome study that allows us to get a better understanding of the correlates of cannibalism in snakes," Glaudas said.

Snakes form a highly successful branch of the evolutionary tree. They are found on all continents except Antarctica and have adapted to most ecological niches, the study authors noted. Because cannibalistic behavior appears in many different types of snakes throughout the world, Falcão said, it might reflect their ability to adapt opportunistically to their circumstances. "It's really surprising for [cannibalism] to evolve independently 11 times in snake lineages," she noted.

The review could not encapsulate all reports of cannibalism in snakes — many are in less-accessible, older books and archives — so there's likely much more to discover on the topic, Falcão said.