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Senses
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Sight Hearing Smell/Taste Touch The 6th sense



Snakes senses range from nonexistent to beyond belief. Please note ahead of time that nothing below is universal for all snakes. There will always be an exception to the rule and each snake has it's senses tuned differently. Below is only a generalized look at their senses.

Sight

Do you see what I see


This sense is not as developed as others, nor should it really. Snakes, being ground crawlers, would have a limited view of their surroundings due to their height, thus having the ability to see great distances would be useless. Useless, that is, unless you were an arboreal snake. These snakes have very well developed eyes and most of them have stereoscopic vision. The reason for this lies in the snake's prey: birds and mammals. Bird eating snakes spend their time coiled on tree branches near areas where birds are known to fly by. These areas could be in an overpopulated rainforest or near a communal nest. The snakes wait with a portion of their body either hanging down or in a striking position and when a bird flies by they strike out to grab them. This kind of precision requires good 3D vision. It's not surprising to note that bird eating or mammal grabbing tree snakes have oversized eyes. Sometimes to the point of rediculousness.

Colour vision can be found in at least some snakes. Tropical versions would be more likely to have colour vision then desert relatives and their skin generally reflects this.

Time of day also effects vision. Nocturnal and crepuscular snakes usually have vertical pupils. A tapetum may or may not be present. Diurnal species generally have rounded pupils although this is not always the case as many boids have vertical pupils and a diurnal existence. Exceptions to the rule.

Hearing

Believe it or not this is one of the most acute senses in snakes.

As most people should know by now (from various documentaries, books and who knows how many TV specials) snakes lack external ears. This is sometimes misinterpreted as having no ears, which is false. Snakes do have ears, inner ears that allow them to hear low frequency airborne vibrations. But snakes have another more acute way of hearing, they hear with their jaw.

Strange as it might sound, it is true. Ground vibrations are transmitted through the snakes body to the quadrate bone (the connection between the lower jaw and skull) where it later goes the middle ear bone (columella) and then to the inner ear.

This means that a snake will always hear you coming before you even see it.

Smell/Taste

Do you smell what I smell


These two senses are grouped here for a reason. The sense of smell and the sense of taste have combined to form one of the most powerful chemosensory devices in the animal kingdom.

Snakes, like all other tetrapods, have two nostrils with which to breathe. Other than breathing though the nostrils don't do much else in the way of smell. Instead snakes have gone a different route, one taken by their lepidosaurian relatives a long time ago. Instead of using only their nose, snakes have adapted their tongue and sense of taste to capturing scent particles in the air and transforming it into olfactory information.

While many lizards have this ability only some truly use it to it's full extent and even then none go to the extremes of snakes. They accomplish this with the help of the vomeronasal organ or Jacobson's organ as it is more commonly called. This organ located at the roof of the snake's mouth, takes in information gathered by the tongue and transforms it into smell, thus making all snakes limbless bloodhounds with scales.

Touch

Touch is another one of the most highly developed of all the serpent senses. As one can imagine touch would play a vital role in the life of a creature that lives on it's belly.

So it is no surprise to hear that snake bodies are flooded with tactile receptors that allow them to feel the slightest change in their environment. This allows for quick changes in muscular movement during locomotion as the snake's tactile receptors sense the slightest shift in the ground.

Tactile receptors also come in handy during social encounters where touch and smell become the communication of choice. Snakes are very responsive to touch.

Heat receptors, the 6th sense

Along with the five main senses (sight, hearing, smell, taste, touch) some snakes have another sixth sense. The ability to sense the heat of other creatures.

The two main groups of snakes have heat sensitive pits. The boids (pythons and boas) and the pit vipers (CROTALIDAE). Although a few other snakes possess this remarkable heat seeking ability, these two are the most prominent.

In boids a row of heat pits are located on the lips in crevices called supralabial pits (top jaw) and/or infralabial pits (bottom jaw). These pits are able to sense slight changes in the ambient temperature, a valuable hunting tool for a nocturnal hunter.

It's all in the lips


Of course not all boids are nocturnal, many are diurnal like Corallus caninus still contain the heat pits. These snakes grab small mammals and birds from tree limbs and it is thought that the heat pits help guide the snakes in their strike. This heat seeking ability would be quite beneficial to a snake that is given only one chance to get it right.

The other group, the pit vipers, have concentrated their supralabial pits into only two super sensitive heat pits and unlike those of the boids, these pits have the ability to actually give a heat image to the brain, so now instead of heat seeking we have heat seeing.

No those are not four nostrils

The pits are comprised of a double chamber divided by a membrane and positioned against a prominenet cavity in the maxillary bones. The pit membrane itself is comprised of a double sheet of epidermis, separated by connective tissue, tiny blood vessels, and free nerve endings from the trigeminal nerve. There is a small pore in front of the eye that connects the inner pit chamber with outer air leaving the outer pit chamber to form the visible pit on the snake's face. These pits are easily mistaken for nostrils thus making the snakes look like they have four instead of two nostrils.

The heat seeing ability of the pits allows pit vipers to hunt their prey in the complete darkness of a moonless night or in the hole of the prey. These pits are so sensitive that a blinded pit viper can sense a mouse that is a mere 100 warmer than the surrounding air from 70cm away. With such a powerful (almost science fiction like) ability it was quickly accepted that these crotalines used their pits for hunting. While this is no doubt true other findings have shown that the pits might serve another function entirely, for that of defense (As mentioned in Snakes: The Evolution of Mystery in Nature, by Harry W. Greene, p. 254-255). It is believed that with the increased parental attention crotalids showed towards their young combined with their rather static defenses, the pits would have been used to help evaluate and track potential threats in their environment.

The chances are quite likely that the pits in crotalids were used for all of the above. Nature rarely gives something only one use.

With senses that range from ordinary (sight) to extraordinary (The Predator like heat seeing) is it a wonder why snakes have come to dominate so many terrestrial habitats?


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