Snakes: General Information

By Carrie Gardner

Snakes branched off the lizard family about 100 million years ago.  However, there is some debate over which family they branched off from.  Most think, it was the Monitor family as they have similar heads and forked tongues. 

 The differences between lizards and snakes are not what you think.  A lot of people believe that because a snake has no ability to blink their eyes, no external ear openings or legs that they are not lizards. when in fact, some species of lizards share these characteristics. 

So what are the differences?  For one, they have a different bone structure in their skull that allows for eating prey items larger than their head (more on that later) and their ventral (or belly) scales are different.  Formed in a row, each end of the scale is attached to a muscle that is attached to a rib.  This allows for locomotion.  Coincidentally, you can count the ribs in a snake by counting those ventral scales.  The ventral scales end at the cloaca (or the vent) which is the common opening for eggs, baby snakes, uric acid and feces.  Beyond the cloaca is the tail of the snake.

Snakes are equipped with special senses and adaptations that allow them to survive effectively.  All snakes can swim or climb trees.  To further that, a lot of species have further adapted to their environments or their prey choices.  There are some sea snakes that never leave the water and some that come out to lay eggs.  Sea snakes' venom is more potent than most snakes' because they don't have the luxury of waiting for the prey to die as do rattlesnakes.  The prey will swim away and with water, it would be hard to follow scent.  There are snakes that are almost entirely arboreal and must be slender and able to get through the branches.  Most of these (and terrestrial snakes) are camouflaged to fit their environments.  Then we have the burrowers who eat only mollusks. 

I'm just going to briefly touch on the senses of snakes in general here.  But remember these descriptions do not apply to all 2,400 species out there.

SIGHT: Generally not very good.  Most snakes can only move their eyes in and out because their eyelids are fixed with a protective scale over the eye.  This is called a spectacle (or a brille) and comes off with each shed.  When a snake sheds, it excretes a milky substance between the two layers of skin to loosen them up right before it begins.  So, right before the shed, their eyes turn cloudy or blue.  It's nothing to panic, just a sign to leave the little fella alone since he won't be able to see at all and might be a little crabby (think of peeling when you're sunburned).

HEARING: Not too good either!  Snakes lack external ears.  They do have middle ears, which enable them to know if they are right side up or not.  They do feel vibrations, though, it is not certain how much.  It does appear that their quadrates (jaw bones) have to be on the ground.  This little hindrance means that snakes have no way to communicate with each other vocally.  All rattles and hisses are for defensive measures only.  It has also been shown that these defensive measures are not used when they're hunting or killing prey.

SMELL: Finally a good one!!  Snakes...ALL SNAKES...depend on this sense the most.  Not only can they smell with their nostrils, but they have this neat little thing called the Jacobsen's Organ.  When a snake is interested in his surroundings, or hot on the trail of dinner, he starts sticking his tongue out.  He does not even have to open his mouth to do it; there is a special notch on the upper lip that allows the tongue to go in and out.  Anyway, he sticks his tongue out and catches air molecules then brings it back up to the Jacobsen's Organ where it processes it and sends it to the brain.  This sense is so important that the tongue is not used for anything else except this.

TOUCH:  I believe that they can feel pretty good.  I know that if my snake is laying on me and I touch him anywhere, he starts moving or reacts, especially around the head and neck.  I would assume for defense purposes their nervous system is pretty good, but this behavior is one I am not sure about.

TASTE: This sense Is all wrapped up with smell and the air molecules (and in some species, heat).  I know, when my snake smells a rat (no pun intended), his little tongue goes faster and faster, until he grabs that rat.

A SIXTH SENSE!: In addition to the five normal senses we are used to, some snakes have an additional sense, infrared heat sensing.  The most sophisticated at this are the pit vipers.  Their heat sensing pit is located between their eyes and their nostrils.  In addition to telling the degree of a prey item to less than a 10th of a degree, they can also tell the ambient air temperature. 

In a study, a scientist covered the eyes of a Eastern Diamondback Rattlesnake.  He put ten mice in and the snake nailed all ten mice.  Next, he covered the eyes and the pits and the snake did not  hit any of what was an enormous amount of mice put in.  Some pythons and boas also have these pits, but they are along their lips or labials.  These are less sophisticated than the rattlesnakes, since the rattlesnakes are considered "New World snakes" and the boids are "Old World Snakes," but they work.  Perfect example, I was feeding my snake, a ball python who has labial pits.  I guess I had accidentally touched his rat because instead of going for his perfectly thawed rat, he shot past it and bit me instead, then twisted his head (OUCH!) and started the coiling.  When I finally untwisted and unattached him from me (he is not full grown yet), I set him in his box and he happily started doing the same thing on the item he was supposed to do it on in the first place.

THERMOREGULATION: Snakes are considered cold-blooded or ectotherms.  Mammals and birds are warm-blooded or endotherms.  Basically, this means that snakes, as well as other reptiles and amphibians, have to move about to different spaces to regulate their temperature. 

They are not really cold-blooded because their body temperature will be near that of the ambient temperature.  In colder climates they will hibernate and go for a period without food.  Otherwise, the warmer their bodies, the more their bodies can do.  Their immune system, digestion, and response time (basically everything) depend on how warm they are.  Once they warm themselves up, they usually go hunting or looking for food or sitting around for food, depending on species.  When they get too warm, they look for bushes, logs or rocky crevices to get their little bodies in to cool off.  Right now, my snake is moving from his cold end cave to his warm end cave.  This is a marvelous system. 

The reason, why snakes and other reptiles don't eat every day, is that their bodies do not have to maintain the heat that we have to.  For humans, it is said, 80-90% of our caloric intake goes towards maintaining our body temperature.  Think about that for a second.  Wouldn't it be nice to just lay in bed and be slow, when it got below a certain temperature?  Snakes have many ways of warming up.  There is ground surface exposure, where they lay out as stretched out as they can and then flatten their bodies for more skin exposure.  Of course, this could lead to easy predation.  Some snakes are dark colored and some have parts (like the head) that are dark.  This usually occurs in colder climates.  In more tropical climates, they really don't have to worry about basking in the sun because the temperatures are just right for them.  Still, arboreal species may climb higher up in the trees to fetch a few more rays. 

I believe, the most dangerous way for snakes to get heat is found in the nocturnal or crepuscular (active at sunrise and sunset) species near paved roads.  Those roads retain heat long after sunset, so the snakes will lay on them to get the last bit of warmth.  Unfortunately, a lot of the poor critters end up as victims of cars.  Snakes can go for months, and, depending on what they last ate (I am talking large constrictors), years, without a meal, as long as they stay in warm places to digest.

HOW DO THEY EAT THAT?  One of the many fascinating things about snakes, is just how much they can stuff in that mouth!  How is that possible?  They have a different bone structure in their jaws to do the deed.  First off, instead of a rigid jaw, they have ligaments attaching the jaw to the skull.  As for their lower jaws, the quadrates do not meet at the chin.  Plus, if you look underneath, you'll see a fold of skin there.  They have extra skin to use to get the sucker in.  What happens is that they do whatever it is they have to do to get their prey, and examine it.  They could be finding the head, or formulating a plan on how to eat this thing.  Finally they sink their teeth in, and "walk" their prey in.  One side unhooks those recurved teeth and goes forward, and then the other side.  Once din din hits a certain point, the muscles shoot it on down to the tummy where some heavy duty enzymes come into play for digestion; powerful enough to go through steel!  Everything is digested and utilized.  After the finish, they yawn (to set everything back into place) and go find some place warm to digest.  Eventually it will come out in the form of feces and uric acid, a white paste they dispel instead of urine.  This is to help preserve their hydration. 

Now here's an interesting question...how do they breathe when they're eating?  Sometimes this swallowing business can take hours.  It is called the glottis.  It is a muscular tube in the front of the mouth that not only holds the tongue but can stretch out to allow for breathing when they are eating.

Carrie Gardner, Secretary