Snakes keep evolving into cannibals — here’s what scientists think is going on
Cannibalism may seem like a rare and unnatural phenomenon, but the behavior has appeared in several lineages of snakes throughout evolutionary history, often triggered by environmental stressors, scientists say.
When researchers examined 500 reports of cannibalistic behavior across snake species, they found that cannibalism evolved independently at least 11 times, according to a study published November 2, 2025 in the journal Biological examinations.
“For us humans, we don’t think of cannibalism as something common – it’s something strange and disgusting.” Bruna Falcaolead author of the study and a graduate student in biology at the University of São Paulo, told Live Science. “But for the snakes, it’s good for them; it’s good for their ecological fitness. … It’s strategic.”
Evolutionary advantages of cannibalism
Some of the most well-known examples of cannibalism in nature are seen in spiders and praying mantises during mating, as may be the case. beneficial for women eat their companions. “Cannibalism is widespread throughout the animal kingdom.” Xavier Glaudasa biologist and National Geographic explorer who was not involved in the study, told Live Science.
Although scientists previously considered this behavior maladaptive – meaning it is not beneficial to a species in general – more and more studies reporting cannibalism in animals are hypothesizing about why the behavior evolved. For example, it could help parents control brood sizeor it could arise in response to limited availability of resourcesa form of population controlor a opportunistic predation choice.
The snakes’ cannibalistic behavior has typically been described in brief, isolated reports, Glaudas said. For example, his research team described Male Montpellier snakes (Malpolon monspessulanus) feeding on female snakes in France – a behavior believed to be due to limited food resources, particularly in times of shortage outside the mating season. (It would be considered unusual for males to eat females during mating season, as this would reduce mating opportunities.)
In addition to being widespread among snakes, cannibalism evolved independently in different snake lineages and regions, according to the study, which combines numerous reports to explain this behavior.
The research team collected 503 reported cases of cannibalism among 207 snake species. The reports covered a wide range of snake groups, as well as all continents where snakes live, including reports of snakes in the wild and in captivity.
“None of us expected snakes to be so cannibalistic, and no one talked about it,” Falcão said. “The more we looked, the more cases we found.”
Cannibalism was most common in the families Colubridae, Viperidae and Elapidae, the team found. Colubridae is the largest family of snakes and accounts for 29% of all reports. Since this family is not generally known to prey on snakes, the authors proposed that most cases of cannibalism in this group may be linked to stressors such as lack of other food sources. Members of the family Viperidae, which includes pit vipers, accounted for 21% of all cannibalism reports. But these were mostly captive cases, the researchers noted, so captivity-related stressors, such as confinement in small spaces with limited food, may have resulted in cannibalism.
Elapidae, the snake family that includes cobras, accounted for about 19% of cannibalism reports. This wasn’t very surprising, the researchers said, because cobras are known to prey on other snakes in the wild.
According to the study, nearly half of cannibalistic snake species have a generalist diet, and researchers have linked this dietary flexibility to cannibalistic behavior when necessary. However, Glaudas suggested that this link may not be clear, since researchers have defined only 47.7% of cannibal snake species as generalists; the evidence for this relationship would be stronger if the percentage were higher, he said.
“Regarding the idea that cannibalism might be more common in generalist species, I’m a little more skeptical of the data presented,” Glaudas said.
Cannibalistic behavior appears to be correlated with jaw structure, so whether a snake has jaws large enough to consume another snake is a key factor; no cases of cannibalism have been reported in snake species lacking this ability.
When researchers analyzed cannibalistic behavior throughout the evolutionary history of snakes, they concluded that the behavior had evolved independently at least 11 times throughout the snake’s evolutionary tree.
Since most reports of cannibalism in snakes are anecdotal, Glaudas said, the study provides useful insight. This is a “welcome study that allows us to better understand the correlates of cannibalism in snakes,” Glaudas said.
Snakes form a very successful branch of the evolutionary tree. They are found on every continent except Antarctica and have adapted to most ecological niches, the study authors note. Since cannibalistic behavior appears in many types of snakes around the world, Falcão said, this could reflect their ability to opportunistically adapt to their circumstances. “It’s really surprising for [cannibalism] evolved independently 11 times in snake lineages,” she noted.
The study couldn’t summarize all the reports of cannibalism in snakes — many are in older, less accessible books and archives — so there is likely much more to discover on the subject, Falcão said.
Source: Falcão, BB, Pedro, VaS, & Entiauspe‐Neto, OM (2025). Occurrence and evolution of cannibalistic behavior in extant snakes. Biological Journals/Biological Journals of the Cambridge Philosophical Society. https://doi.org/10.1111/brv.70097
