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A new paper published in the open-access journal Herpetozoa records a rarely documented event in the world of snake predation: an adult female Common European Adder (Vipera berus) attempting to kill and swallow a young European Hare (Lepus europaeus) nearly ten times its own mass.
Watch below (warning: contains footage some may find distressing):
The incident, observed on the Danish island of Læsø in August 2022, saw the adder, which was likely in a state of nutritional deficit after giving birth, attack a young hare (a leveret) in open grassland. Researchers Henrik Bringsøe, Daniel Jablonski, and Klaus Birch document the interaction in their research paper.
The snake was seen biting and examining the hare’s limbs and head, which is how adders assess whether prey can be swallowed. Despite the adder’s determined efforts, intervention from the observer prevented the snake from attempting ingestion, and the hare succumbed to its injuries shortly after. The research paper’s authors suggest it is likely that, without intervention, the snake would have abandoned its excessively large prey after careful examination anyway.
The sheer size difference between predator and prey makes the observation noteworthy. The adder, estimated at 60 cm in length and weighing around 110 grams, was facing a hare of about 30 cm and 1,000 grams.
Such attempts at oversized prey are not unknown among snakes, but they are poorly represented in scientific literature and may be more common than previously thought. Snakes often abandon prey that proves impossible to consume, but these events are seldom reported.
The authors contextualise this event with similar cases from around the world, including rattlesnakes and other vipers attacking animals too large to swallow. Sometimes, these ambitious meals can even prove fatal for the snakes themselves. The paper suggests that the drive for a high-energy meal, particularly after energetically costly events like giving birth, may push snakes to take such risks.
Lead author of the study, Henrik Bringsøe, has a history of recording rare and entirely new snake feeding behaviour, such as snakes disemboweling and feeding on the organs of living toads, and two snakes playing tug-of-war with a limbless amphibian.
This remarkable observation highlights the need for more documentation of such underreported phenomena in snake ecology, and serves as a reminder that in the wild, even the most experienced predators can be a little too optimistic.
Original source
Bringsøe H, Jablonski D, Birch K (2025) Overly optimistic adder, Vipera berus (Linnaeus, 1758), killing and intending to swallow an oversized young hare, Lepus europaeus Pallas, 1778. Herpetozoa 38: 155-159. https://doi.org/10.3897/herpetozoa.38.e143850
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