In 2024, eastern garter snakes passed a scent-based self-recognition test: 24 snakes investigated their own altered scent, suggesting self-recognition

Scientists have long asked whether reptiles can recognize themselves. Do they just do things because they have to survive? For a time, most scientists thought that only mammals and birds could really understand themselves. Researchers who study animal cognition conducted new research using scent, the sense snakes rely on most, to navigate the world.

How eastern garter snakes use scent to test self-recognition

For more than fifty years, people used a simple test to see if animals knew they were themselves. This test was called the mirror self-recognition experiment. In this test, scientists marked an animal's body with dye. They then watched to see whether the animal would use a mirror to inspect the mark. Animals that rely heavily on sight, such as monkeys, dolphins, and elephants, have tended to do well on the test. Animals that rely more on smell, such as snakes, have not done as well. Snakes have limited vision, so they use their tongues to sample chemical cues in the air.


Some scientists argued that the test disadvantaged animals that rely on smell. Researchers therefore developed a test designed for snakes. This test used scent cues instead of mirrors. The scientists wanted to see whether eastern garter snakes could distinguish their own scent from other scents. According to the National Institutes of Health, animals that live in groups may recognize themselves when tested in ways suited to their behavior. In this test, the snakes did not have to look in a mirror. Instead, they smelled different scents to see if they could pick out their own smell.

Inside the chemical self-recognition experiment

A study titled 'Olfactory self-recognition in two species of snake,' published in the journal Proceedings of the Royal Society B: Biological Sciences by researchers from Wilfrid Laurier University, examined 36 eastern garter snakes, along with 18 ball pythons. They collected skin oil from each snake. They placed it on different pads in three conditions: each snake's scent mixed with olive oil, olive oil alone, and another snake's scent mixed with olive oil. The scientists recorded how often each snake flicked its tongue toward each scent. This is how snakes gather information about their surroundings. The African ball pythons checked out all the pads. They spent the same amount of time on each one. The eastern garter snakes showed the strongest interest in the pad containing their own scent, compared with the plain-oil pad or another snake's scent.

In a separate phase of the same study, researchers tested a subset of 24 of the eastern garter snakes by placing them in cages with scented cotton pads or swabs carrying a modified version of their own scent. The snakes spent more time investigating scents that were similar to, but not exactly the same as, their own. This pattern suggests the snakes could tell when their own scent had been altered and were motivated to explore it further, though the study stops short of claiming the snakes were consciously aware of this.

How social living may shape cognition

Eastern garter snakes responded to the chemical self-recognition test, while ball pythons showed no preference. Researchers think this difference may be linked to the two species' social behavior. Garter snakes are social, often gathering in groups during the winter months and living in communal dens, where they interact with one another using chemical trails, so they need to distinguish themselves from others when living in close quarters. Ball pythons, by contrast, are semi-arboreal ambush predators that don't brumate and rarely interact with other ball pythons except to mate, so they may have less need to tell themselves apart from others. Eastern garter snakes respond to changes in their scent, suggesting that social living may shape how animals respond to self-related cues.

What the findings may mean for animal cognition

The 2024 finding prompted researchers to rethink self-awareness in animals. For a time, people thought reptiles were simple creatures that acted mainly on instinct. That view reflected limited understanding of reptile behavior. Scientists have been learning more about reptile cognition by studying animals in ways that reflect their natural behavior. Passing a smell-based test does not mean a garter snake thinks about life the way humans do. It does suggest that the snake can distinguish itself from other stimuli, which may reflect a complex cognitive ability.