Most of us likely consider snakes to be cold, solitary beings, as indifferent to others of their kind as they are to us.
But those notions are wrong—especially when it comes to garter snakes, a new study says.
These nonvenomous creatures, which range from the chilly plains of Canada to the forests of Costa Rica, have definitive preferences about which snakes they hang out with—in other words, they have “friends.”
“All animals—even snakes—need to interact with others,” says study leader Morgan Skinner, a doctoral candidate in behavioral ecology at Wilfrid Laurier University in Canada. To investigate this theory, Skinner devised a novel experiment to assess the personalities and sociability of eastern garter snakes (Thamnophis sirtalis sirtalis).
The results showed that “like us, they seek out social contacts, and they’re choosy about whom they socialize with,” says Skinner, whose study appeared recently in Behavioral Ecology and Sociobiology.
The idea that snakes have close friends may be surprising, but such relationships are increasingly being found throughout the animal kingdom, from flamingos to bats to elephants. A recent analysis of vampire bats showed, for example, that bats and humans both have conditional friendships.
Scientists are likely better at discovering friendships among animals now than, say, 30 years ago, partly because many societies are more accepting of such a concept, and because researchers have far better tools for gathering and analyzing the data.
Analyzing social networks in wildlife, such as snakes, “has made huge leaps in the last few decades,” says study co-author Noam Miller, a comparative psychologist and Skinner’s advisor.
Indeed, as this field of study deepens, it’s now common to use the word “friend” when discussing such relationships in nonhuman animals.
That wasn’t the case even as recently as 2012, says Melissa Amarello, a herpetologist and director of Advocates for Snake Preservation, who was advised against using the word in her thesis on closely bonded black rattlesnakes in Arizona.
“It’s really cool to see this study,” she says.
Snakes in a shelter
For the research study, Miller and Skinner observed 40 juvenile eastern garter snakes—30 from wild-caught mothers and 10 from a single litter purchased from a breeder.
To keep track of the reptiles, Skinner marked each with a pattern of nontoxic colored dots on its head. In his lab, he placed a batch of 10 snakes—a mix of males and females—inside a walled, tabletop enclosure that included four plastic shelters with small entrances. Because there were only four shelters, the 10 snakes had to form groups.
For eight days, from 7 a.m. to 7 p.m., a camera recorded an image of the testing arena every five seconds, tracking the snakes’ movements. Twice a day, Skinner also photographed the snakes and their groupings. He then removed the serpents, cleaned the enclosure to eliminate any odors, and put the snakes back—but in different places. (See National Geographic's amazing snake pictures.)
The snakes, though, had other ideas. They didn’t stay where Skinner placed them, but returned to their original groups of three to eight individuals inside the small shelters. What’s more, they sought out specific snakes that they’d hung out with before.
“They have sophisticated social cognition,” adds Miller. “They can tell others apart.”
The scientists also tested the snakes’ personalities—namely, whether they were “shy” or “bold,” the two main traits evaluated in wildlife. To see if an individual garter snake was bold, they put it in a shelter alone.
Shy individuals tended to stay put, and rarely ventured into the larger enclosure. Bolder snakes behaved like explorers, often immediately leaving the shelter to slither about their new habitat. (Here’s the secret to how snakes slither.)
However, once they were in groups, such personality differences vanished, and the snakes generally followed the herd—perhaps a strategy to keep safe in the wild.
Of course, the experiment is limited in that it was done in captivity. “Animals behave differently in captivity, so I’m left wondering how this translates to natural conditions,” notes Amarello.
Because wild garter snakes form aggregations similar to those they created in the lab, however, Miller and Skinner suspect such relationships occur in nature—and are common in many reptilian species. (See beautiful photos of amphibians and reptiles.)
Cryptic loners? Think again.
Though animal buddies are making the news these days, Miller cautions that animal friendship “may have nothing to do with the reasons humans have friends.”
Indeed, the scientists have no idea what’s motivating friendships in garter snakes, though they do know it’s not related to reproduction or mating: The study snakes did not prefer the opposite sex as friends.
But such partnerships must be offering some benefit—otherwise the animals would not waste the energy forming such bonds. For instance, snake friends usually curl up together, which helps them retain heat and defend against predators.
Whatever the reason, says Gordon Burghardt, an evolutionary biologist at the University of Tennessee, the study “should help convince people that snakes aren’t all cryptic loners, but have more social intelligence and a larger social repertoire than most of us realize.”