Can Snakes Recognize Themselves? One Species Has Passed a Modified ‘Mirror Test’ Based on Smell

Eastern garter snakes might recognize their own scents, suggesting the reptiles are more cognitively complex than thought, according to a new study

A close-up of a black and yellow eastern garter snake in a patch of grass.
In a modified version of the mirror self-recognition experiment, eastern garter snakes showed signs that they recognize their own scent. Mark Nenadov via Flickr under CC BY 2.0 DEED

For decades, scientists have used the “mirror test” to determine whether different species are capable of self-recognition. In it, researchers observe whether animals, when marked with paint somewhere on their body and placed before a mirror, investigate the artificial spot. Passed by primates, dolphins, elephants and even certain fish, the test has been thought to measure social intelligence.

Now, scientists have carried out a new spin on the experiment with two species of snakes. Because of the reptiles’ poor vision, researchers tweaked the typical mirror test to appeal to their sense of smell. In findings published this week in the journal Proceedings of the Royal Society B, a team of three scientists doctored the snakes’ own scents and observed whether the creatures recognized—and were curious about—the change.

“There’s a bias out there that [reptiles are] these boring, not very cognitive animals, and that’s completely wrong,” Noam Miller, a co-author of the study and a psychologist at Wilfrid Laurier University in Canada, tells the New York Times’ Asher Elbein. “That’s one of the reasons why we got very interested in studying them and showing the complex cognitive things they can do.”

The researchers tested 18 African ball pythons, a solitary snake species, and 36 eastern garter snakes, which are known to be more social. They collected body oil samples from the snakes and set each one in a long testing arena.

Five cotton pads soaked with different scents awaited them there: The snake’s own scent, its own scent mixed with olive oil, pure olive oil, the scent of another snake and the scent of another snake mixed with olive oil. By recording how long the snakes flicked their tongues—the reptiles’ way of smelling, tasting and, in many ways, “seeing”—the team gauged their interest in each scent.

An eastern garter snake, stretched to its full length on a gravel road, flicks its red tongue
Snakes, including the eastern gartner snake pictured, flick their tongues to smell by gathering chemicals from the air. Paul Hurtado via Flickr under CC BY 2.0 DEED

African ball pythons spent a similar amount of time with each odor. But eastern garter snakes paid much more attention to their own odor that had been mixed with olive oil. The scientists suggest the garter snakes recognized themselves and were intrigued by the unexpected change in their smell.

“They only do long tongue flicks when they’re interested in or investigating something,” Miller tells New Scientist’s Chen Ly. “They may be thinking: ‘Oh, this is weird, I shouldn’t smell like this.’”

Other researchers don’t go so far as to say the snakes were capable of self-recognition. “This interpretation only becomes plausible if a correlation with social behavior can be established,” Johannes Brandl, a philosopher at the University of Salzburg in Austria who was not involved in the study, tells New Scientist.

But Rulon Clark, a biologist at San Diego State University who also was not involved in the study, thought the findings were meaningful. “In a lot of ways, I think their experimental paradigm is more powerful than the mirror tests,” he tells the New York Times. “A highly reflective mirrored surface doesn’t have a lot of ecological analogues. But encountering and understanding the importance of chemical cues left by yourself and your conspecifics is probably a deeply important aspect of the natural history of these animals.”

The study corroborates findings published in the journal Behaviour in 2021, in which a team of University of Tennessee, Knoxville, researchers conducted a similar chemical-based recognition study with 24 eastern garter snakes. Instead of scents and olive oil, they observed the snakes’ interest in cage liners—their own, versus those of other snakes with both similar and dissimilar diets. By observing how long a snake flicked its tongue before each liner, that team also showed that the snakes homed in on their own scents more than any other.

“Snakes demonstrate many of the same cognitive and perceptual mechanisms as other animals if you study them in the right way, ask the right questions and respect their biology and way of dealing with the world,” Gordon Burghardt, a comparative psychologist at the university and the study’s lead author, told National Geographic in 2022.

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