Cannibalism, often viewed as a disturbing and unnatural behavior, is surprisingly common in the snake world. New research reveals that this practice has evolved independently across numerous snake lineages, suggesting it’s not a rare aberration but a strategic adaptation driven by environmental pressures and opportunistic feeding habits.
A comprehensive review of 500 reports spanning 207 snake species, published in in Biological Reviews, found that cannibalism has emerged independently at least 11 times throughout snake evolution. This challenges the previous understanding of cannibalism as an infrequent and accidental occurrence.
“For us humans, we don’t think of cannibalism as something common –– it’s something weird and disgusting,” explains Bruna Falcão, lead author of the study and a graduate student in biology at the University of São Paulo. “But for snakes, it’s good for them; it’s good for their ecological fitness. … It’s strategic.”
Evolutionary Advantages and Context
While cannibalism is observed across the animal kingdom – including instances in spiders and praying mantises where it can be beneficial for females – the prevalence in snakes is particularly noteworthy. Scientists are increasingly recognizing that cannibalism isn’t necessarily maladaptive, but can serve several purposes. These include controlling brood size, responding to limited resource availability, and simply representing an opportunistic predation choice.
Previously, reports of snake cannibalism were often isolated incidents. However, this new research demonstrates a widespread pattern. For example, research has documented male Montpellier snakes (Malpolon monspessulanus) in France consuming females, a behavior thought to be linked to food scarcity outside of the mating season. Eating a mate during the mating season, however, would be counterproductive.
The study found that cannibalism is most frequently observed in snakes belonging to the Colubridae, Viperidae, and Elapidae families. Colubridae, the largest snake family, accounted for 29% of reported cases. The researchers suggest that, because this family isn’t typically known for preying on other snakes, instances of cannibalism within this group may be more closely tied to environmental stressors like limited food sources. Viperidae (vipers) comprised 21% of reports, but these were often observed in captivity, suggesting that confinement and limited resources may contribute to the behavior. Elapidae (cobras) accounted for approximately 19% of cases, which isn’t surprising given that cobras are known to prey on other snakes in the wild.
The research also indicates a correlation between dietary flexibility and cannibalistic behavior. Nearly half of the snake species exhibiting cannibalism have generalist diets, suggesting they are more likely to turn to other snakes as a food source when preferred prey is scarce. However, some researchers caution that a stronger correlation would require evidence demonstrating a higher percentage of generalist diets among cannibalistic species.
A key physical factor appears to be jaw structure. Snakes must possess jaws capable of expanding to accommodate another snake as prey; no cannibalism has been reported in species lacking this ability.
A Changing Perspective
The sheer number of documented cases – 503 instances across the 207 species analyzed – surprised the researchers. “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.”
While the review provides a valuable overview, researchers acknowledge that it doesn’t encompass all instances of snake cannibalism. Many reports remain buried in older books and archives, suggesting there’s still much to learn about this behavior. As Xavier Glaudas, a biologist and National Geographic Explorer who was not involved in the study, notes, this research is a “welcome study that allows us to get a better understanding of the correlates of cannibalism in snakes.”
The adaptability of snakes is well-established, with these reptiles thriving on all continents except Antarctica and colonizing diverse ecological niches. The prevalence of cannibalism across various snake types and geographic locations suggests it’s a testament to their ability to adapt opportunistically to challenging circumstances. “It’s really surprising for [cannibalism] to evolve independently 11 times in snake lineages,” Falcão noted.
This research underscores the complexity of animal behavior and challenges preconceived notions about what is considered “natural” or “unnatural.” It highlights the importance of continued research to understand the ecological factors driving these behaviors and the role they play in the survival of species.
