Why Do Snakes Flick Their Tongues?

Having no arms or legs, flippers or wings, snakes are at a distinct disadvantage in the animal kingdom. But they are not without resources. The forked tongue and the complex vomeronasal organ, also called the Jacobson's organ, play a big part in the success of a snake's ability to thrive. When looking at a snake head-on, it would appear that the tongue is very small because you only see the tip of it. The tongue emerges from an accommodation of the upper lip that obviates the need to open the mouth. All snakes have a forked tongue, but some are technically only "notched" and not split down the middle. The tongue is actually much longer than it appears and is coiled inside the snakes lower jaw when not in use. Snakes also have nostrils and a nose which are used for smelling and breathing, just like in all other animals.

The Jacobson's organ is named for Ludvig Levin Jacobson, an anatomist who first discovered the presence of this tiny organ in 1811. It is fully developed in reptiles, and those with deeply forked tongues use it more often than those with only slightly forked tongues. It is also present, to a much lesser degree, in other species, including humans. It refers to a small patch of highly sensitive olfactory cells and two tiny holes located on the roof of the mouth, or palate. If you've ever seen a cat grimace, or appear to hold his mouth open in an unusual manner after sniffing an object, you've seen a cat using his Jacobson's organ in an act called the Flehmen response. Lions use it during mating season.

The action of flicking the tongue helps the snake smell the air around him. In addition to his olfactory senses, he also has use of the vomeronasal organ. When the snake extends his tongue, he collects odors in the air. All odors produce chemical molecules. In humans and other animals, the nose filters these microscopic particles, and it does in snakes as well. The snake's tongue, however, collects these odorants, which adhere to the tongue. The tongue is then brought back into the mouth where these unfiltered, intact molecules come into contact with the highly sensitive olfactory cells that comprise the Jacobson's organ and the olfactory nerves via the two tiny holes. The flicking tongue speeds this process and tells the snake about his environment.

The reason for the forked tongue has been the subject of much debate and wonder for centuries. The Greek philosopher Aristotle postulated that it was so the snake could savor his food. Later scientists came up with other theories, including the idea that it was a complex fly-catching device. According to the Society for Integrative and Comparable Biology, however, its purpose is to collect odorants from all directions. The tongue flicking is such a fast motion that most humans wouldn't be able to tell that not only is the tongue moving in and out, but the forks are actually oscillating as well. The split tongue also helps the snake know from which direction the odor is coming so he knows where to locate his next meal.