Reptile Expert

Snakes

Green Vine Snake

Green Vine snake, image by nasmac (flickr)

In the world there are known to be in excess of 2000 snake species which all belong to the order of Squamata alongside the lizards. Fossilised remains of snakes are incredibly rare due to their fragile nature. This being said, an evolutionary history of the snakes has been put together by biologists studying the rare fossilised remains which are still in tact and by analysing the similarities that exist in the living snakes of today. Palaeontologists have put forth evidence that seems to indicate that snakes evolved from amphibians which are called Labrynthodonts.

Internal structure

The majority of a snake’s structure internally is modified because of the way the body is formed in its notable long slender exterior. The skeletal arch that supports the hind limbs of most vertebrates (formally known as the pelvic girdle) is most commonly not seen in a lot of snakes.

Locality

Snakes inhabit almost every single region on the planet. However the most common location that a snake can be found is in Africa and Australia, as there mild climates create a sustainable environment for them to survive and breed in, meaning an abundance of snakes.

Despite being cold blooded animals with the ability to sometimes survive harsh sub-zero temperatures for many weeks on end (the prime example of this is the garter snakes, which group together over winter surviving sub zero temperatures), as a general rule snakes very rarely inhabit colder climates. This is because prolonged periods of time spent in such environments have an adverse effect on them; they will often become very sluggish due to the fact they are cold blooded. However one of the species typically known to inhabit and thrive in fierce sub- zero temperatures is the garter snake.

Garter snakes have a very effective method of avoiding the below freezing conditions of their surroundings, they avoid the winter weather (and freezing temperatures) by looking for rocky areas in which they will burrow and seep into the fissures in the ground. As long as they go below the frost line they are be able to survive.

The Garter snake also lives in Alaska and belongs to the family of Thamnophis, they are the only snakes to live in Alaska, and as far south as Central America. They are also totally harmless to humans as upon seeing humans they will recoil in fear and hide as they are known for their shy and timid characteristics.

Snakes are the 'most recent stage' (ie the most recent large physiological fork in the evolutionary line) in the evolution of reptiles, they are from an evolutionary perspective, the newcomers if you will. They are descendants of the lizard, losing their legs in the process meant snakes would have to develop an effective method of travel which resulted in something both unique and distinctive. There are four known methods of travel that snakes use to “get around”:

Concertina: This is achieved by a snake using sections of its body to anchor while other sections of the snake are used to propel in the desired direction of travel. The sections of the body which are anchoring and used to propel alternate which results in movement. This is very difficult for the snake and not the fastest way to move.

Serpentine: This is the technique that often comes to mind when you think of a snake getting from A to B, it’s the wavy motion that is achieved by pushing off the surfaces within the snake’s landscape.

Side winding: Think of how an inchworm moves, well this resembles how snakes use side winding to move, a snake will raise the centre of its body and then force it down which moves it in a very strange fashion, a snake that has honed this skill is the suitably named “Sidewinder”.

Rectilinear: this is a straight movement, not particularly fast in nature this movement is achieved by using the larger scales on the under belly to hold the ground whilst the other scales act in a way that enable it to move forward.

Snakes are exclusively carnivorous in nature and usually have 2-3 food types which dominate their eating patterns. Their prey can vary from such animals as rodents, insects, fellow evolution “buddies” such as lizards and even other snakes (most notable for this care the king snakes)!

Snake are also known for their rather unique method of eating. If they are confronted with large prey/food which at first glance seemingly wouldn’t fit in their mouth they will actually are specially adapted to extend their jaw (a common misconception is that they dislocate it, this is not true) which at first glance you wouldn’t think was on the menu. Snakes are versatile in their efforts to consume prey in the sense they will eat food whilst it is still alive, asphyxiate prey constricting it until the restriction of air flow causes inevitable death, or as you would expect, inject venom using their infamous fangs into the unsuspecting victim.

Sensory perception

Snakes use senses such as sight, touch (namely vibrational information) and what can largely be thought of as smell to detect their prey and also to detect possible threats within their natural environment. Snakes smell by tasting the air around them, this is how they determine possible threats and prey and differentiate between the two, smell is particularly important in prey detection. When snakes flick their tongue in and out in a well known fashion, this is how they collect the particles the information of which is processed in the Jacobson’s organ for analysis. The reason snakes have splits in their tongues is because the tongue must touch the two pits which are themselves split and located in the roof of the mouth. An indication of the amount a particular species relies on its Jacobson’s organ or Vomeronasal organ. Is the Depth of the fork in the tongue, a smaller fork commonly indicates a lesser dependence on the organ. The reason the tongue is forked is the same reason that we have two nostrils, they allow additional directional information to be collected. For instance, if there are more ‘smell particles’ on the left nostril it alerts the snake to the fact that the prey is to the left, and the snake can act accordingly. Our noses work in the same way; it is how we are able to pinpoint the source of a smell.

There are different varieties of tongue flick techniques that snakes use. The method usually depends on the snake’s environment. If it is well suited and aware of its surrounding and the inhabitants that dwell within them short flicks of the tongue will only be necessary to access any changes of concern in the habitat. Where as a snake which is often changing location, to hunt for instance the tongue is extended further and the range of the flick is extended in the attempt to process as much information as possible. For more information on snake senses check out our snake senses page, and also our infrared sensing page.

Green Vine Snake