10 Facts About How A Snake Can Smell

The World of Snake Smell-Tasting

When you ask people what creeps them out about snakes, it's often something like, "They're slimy" (which they aren't) or "When the stick their tongue out at me it's scary." This got me to thinking about an idea for this blog  post, because most people don't really understand why a snake sticks it tongue out at you and what it's really doing. There's a lot more going on than snake razzberries or just "smelling", especially when the tongue goes back in the snake's mouth. So, here are 10 facts about how a snake can smell:

1. Snakes lack an outer ear and eardrum, they can't focus their eyes well, and their sense of touch is limited (think hard scales). 

Snakes, and some lizards, rely primarily on their senses of smell and picking up vibrations through the ground. Watch a snake carefully, and once it senses vibrations it will start to flick its tongue out of its mouth.

2. A snake has a groove in its top lip that lets its tongue go in and out without opening its mouth.

This grove is called the rostral groove and is a handy little notch that sits in the upper lip, between the two nostrils.

 

3. It is a common myth that snakes are trying to "sting" you when they stick out their tongue. 

Very few snakes actually have venom, and of those that do they deliver the venom through a bite and needle-like teeth that are in their mouth, not their tongue. They can't sting or disperse venom with their tongue.

4. A snake's tongue can neither smell or taste. The tongue doesn't have smell receptors or taste buds (those are somewhere else...wait for it...).

Snakes use their tongues to take a sample of molecules in the air (think of chemical collection). They are "taste testing" the air for smells and pheromones, but the tongue can't "read" the information by itself.

5. A snake has a forked tongue to collect air samples from different directions.

This forked tongue allows the reptile to sense specific smells from different directions. It can take air samples quite rapidly (as evidenced by the quickly flicking tongue), which can help it hone in on a smell's location.

6. The longer the forks of the tongue of the snake or lizard, the more it uses its sense of smell-tasting.

After a snake sticks its tongue in the air, the tongue is retracted through the lip notch and into the mouth. There the "smell" chemicals are mixed with fluids in the mouth, and the tips of the tongue are placed into a special smell/tasting organ. The longer the two forks, or tines of the tongue, the more the animal relies on smell to help it find prey or move around.

For example, the green iguana has a very small fork in its tongue, while snakes like garter snakes have very long forks in their tongues, see the images below:

7. There are two holes in the inside of a snake's mouth, on the upper palate, called a Jacobson's Organ, into which the snake's tongue is placed to receive taste/smell information.

This organ is also called the vomeronasal organ (VMN). It works by sensing chemicals and pheromones that are picked up by the tongue. When the snake's tongue enters its mouth it sticks the two forks of its tongue into two tubes that are the "organ." These two tubes also help with directional smell/taste information. Once stimulated, this organ then sends signals through nerves into the olfactory bulbs in the snake's brain.

 

8. Snakes uses taste/smell information from their tongue to track prey and find dens. The males also use it to find females by tracking pheromones.

It's been found that if the Jacobson's Organ is disrupted then the snake has a hard time finding prey. In one study rattlesnakes couldn't find prey that they had already struck.

9.   Snakes have different types of tongue flicks to collect smell/taste information.

Snakes may use different tongue flicking motions to collect information. Some snakes flick their tongue side to side, as they move along the ground, to pick up scent trails. Some may pick up air borne chemicals my moving their tongue in short up-down patterns without touching anything (just air). It's thought that like a paddle or oar moving through water that this creates "air vortices" that help circulate air towards their tongue. Some snakes even use more modulated up-down oscillations to track scents, especially during breeding season. This oscillation is though to increase the amount of air that goes over the tongue and increase accuracy in tracking.

10. Humans and many other animals have a Jacobson's Organ too!

Yes, even you have a Jacobson's Organ, you just didn't know it. It's found in most four footed animals, including cats, cows, dogs, deer, seals, tigers, etc. It's also present in marsupials and primates. Like in snakes it's found in the lining of the roof of the mouth. Before you go checking to see if you have two holes like a snake, you don't. You can't feel them with your tongue. Your vomeronasal holes are at the base of the "nasal septum" and you can't get to them without a camera (which I wouldn't advise). They are opening that lead to a "pit" of tissues.

Here you can see a picture of a human VMO from an article in the International Journal of Morphology (v.26, n.2. 2008).

There's a lot of debate as to whether this "pit" of tissue is stimulated by human pheromones. Some say yes, some say it's a dead end. What do you think?