Sea Snakes Attacking Humans Probably Just Horny, Scientists Say

Picture yourself snorkeling or scuba-diving along a lush coral reef, abundant with color and life. All of a sudden, this serene underwater experience morphs into a horror show as an aggressive sea snake slithers into view and attacks you for no apparent reason.

Should you ever face this scary situation, ocean scientists have some sage words of advice: don’t panic and stay still, because the snake may just be trying to mate with you.

That’s the upshot of a new study led by Tim Lynch, a senior research scientist at Australia’s Commonwealth Scientific and Industrial Research Organisation, which is based on his 158 encounters with olive sea snakes (Aipysurus laevis) as a diver in the Great Barrier Reef. 

Lynch and his colleagues observed that unprovoked aggression from these animals almost always involves males during the breeding season, suggesting that these encounters are a result of “mistaken identity during sexual interactions,” according to a study that offers “the first quantitative evidence on sea snake ‘attacks,’” published on Thursday in Scientific Reports.

These insights about olive sea snakes were recorded in dives Lynch conducted from 1994 and 1995, but it wasn’t until the coronavirus pandemic hit in 2020 that the opportunity finally arose to publish the results.

“You can blame COVID for this,” said Richard Shine, a professor of biology at Macquarie University and an emeritus professor at the University of Sydney who co-authored the study, in an email. 

“Tim Lynch did the work as part of his PhD,” he continued. “I examined his thesis in 2000, thought it was great, but he never published it. Stuck at home with COVID, I contacted Tim to ask if he was interested in collaborating with me to turn bits of his thesis into published papers. He agreed (bless his heart!), and this is the first one.”

Though Lynch captured this data decades ago, the lessons from the study remain just as relevant today. Sea snake attacks are rare, but they can be fatal, according to another recent study that Shine co-authored. 

Some snake species are extremely venomous, including olive sea snakes. Victims tend to be fishers because “snakes caught by fishermen are stressed and can’t escape, so they retaliate,” Shine noted. However, recreational swimmers and divers could be threatened by encounters as well: even if a snake doesn’t bite a diver, the panic from an unprovoked attack could put the person’s life at risk.

It’s easy to see why a sea snake that has been captured by fishers would retaliate and defend itself, but Lynch, Shine, and co-author Ross Alford, an ecologist at James Cook University, wanted to understand the motivations behind unprovoked attacks. The authors note that it is extremely rare for snakes that live on land to charge or bite people for no reason, making this behavior in their marine relatives something of an anomaly in the larger snake family.

By examining diver reports and Lynch’s own observations, the researchers discovered that aggression toward humans almost always occurred during the winter breeding season, which lasts from May to August. Males approached humans much more often than females, and displayed behaviors that could be related to courtship, such as coiling around a diver’s limb. 

“Agitated rapid approaches by males, easily interpreted as ‘attacks,’ often occurred after a courting male lost contact with a female he was pursuing, after interactions between rival males, or when a diver tried to flee from a male,” the authors wrote in the study. 

These encounters suggest that a “reproductively active male, highly aroused, mistakes the diver for another snake (a female or a rival male),” they added. “At first sight, the idea that a snake might mistake a human diver for another snake seems ludicrous, given the massive disparity in size and shape between those two objects. Nonetheless, this offers the most plausible explanation for our observations.”

Indeed, the study suggests that sea snakes may have poor eyesight compared to land snakes, which could also explain the rare instances of females charging divers. These females were often fleeing from pursuant males, and may have mistaken humans for coral formations that they could hide behind.

As tempting as it might be to try to escape these encounters, the team notes that a sea snake might give chase—and you are simply not likely to outswim these speedy ocean animals. The best course of action is for the person to stay still and let the snake explore them by “tongue-flicking,” or even making contact with the skin or wetsuit, which is likely to de-escalate the conflict as the animal realizes its mix-up.

“If mistaken identity underlies most ‘attacks’ by sea snakes on divers, the best strategy for divers in such a situation may be to allow the snake to investigate them and in particular to allow for the snake to investigate chemical cues with its tongue; a bite is unlikely unless the animal is threatened or injured,” the team said in the study. “Attempting to flee is likely to be futile and may even increase the ardour of the pursuit; and attempting to drive the animal away may induce retaliation.”

Shine and his colleagues also point out that male sea snakes are far from the only species that “court inappropriate objects,” in the words of the study, and provide many colorful examples of other mistaken courtship attempts. Dolphins, dugongs, sea lions, and sea turtles have all been observed attempting to copulate with humans, and “some beetles famously court beer bottles,” the study notes.  

Shine hopes that these recent studies into sea snakes will motivate people to better understand these mysterious and important marine animals.

“Sea snakes are very understudied, so the potential is huge,” he said.