S n a k e Basics 2

Snake History and Evolution

It is thought that snakes first appeared between 100 and 150 million years ago. No one knows exactly what the ancestors of snakes are, but it is assumed that it was some type of lizard that started to burrow into the ground, and eventually lost its legs because it didn't need them anymore. Certain species of lizards such as skinks (Scincidae), and anguids (Anguidae), have even shown a tendency of their legs to get smaller or even completely disappear. Current opinion is that monitor lizards are the ancestors of snakes. There is some evidence to support this theory; for instance, both snakes and monitor lizards have the forked tongue and Jacobsen's organ to scent their prey. Although at the present, there are no known monitor lizards without legs (if you have one, drop me a line) that doesn't mean that there never was a monitor without legs; they may have become extinct along the way.

The fossil record of snakes is incomplete; very early snakes were similar to burrowing snakes of today (wormsnakes, blindsnakes), so the bones were very delicate, making fossilization all but impossible. Snakes have gone through a long process that we only have fuzzy idea of. More "primitive" snakes, such as boas and pythons, have spurs (vestiges of legs), on each side of the cloaca; apparently males use them to aid in mating. Snakes considered most primitive include:

• boas and pythons (boidae)
• blind snakes (typlopidae)
• threadsnakes (leptotyphidae)
• animalepids (animalepididae)

Colubridae is the largest family of snakes with an estimated 1,500 species. It is sort of lumped together, though undoubtably in the future it will be broken into smaller families. Most colubrids are non-venomous and harmless, although some colubrids loosely called back-fanged snakes are venomous. They have enlarged, grooved teeth at the back of the mouth connected directly to the venom glands. Prominent examples of back-fanged snakes are: the hognose snake (I bet that was a surprise), the mangrove snake, and the boomslang (one of the few colubrids which are known to be able to kill people). Even though this group of snakes are venomous, most are not harmful because of where their fangs are located and their venom is usually weak.

Viperidae is another large family of snakes with 220 distinct species that live in both the Western and Eastern hemispheres. Most vipers are heavily built and have large heads that aid them in eating very large prey. Vipers have folding fangs that unfold when they open their mouths wide. There are two main sub-families of Vipers: Viperinae and Croatalinae. The former are the "true" vipers (such as Rhinoceros vipers and Gaboon vipers) and the latter are the "pit" vipers (such as rattlesnakes, copperheads, bushmasters). Some people classify these 2 sub-families (Viperinae and Crotalinae) as each having its own family. Rattlesnakes are considered by many to be the most advanced and recently evolved snakes, as they have adapted so that they have rattles on their tail to warn large animals that might accidentally step on them (not accidentally in certain species).

The Ectothermic Snake

Most snakes prefer a temperature range of between 70°F and 95°F (21°C and 35°C, respectively), but snakes cannot internally reproduce or regulate their body temperature sufficiently. So instead, snakes maintain their temperature through a combination of behavioural and external methods. One example of an external method is if a snake is too cold they would move to some place hotter (pretty simple!), and vice-versa. A behavioural method would be like flattening themselves out so more of the sun hits them, or that many snakes group together to conserve energy. Although snakes rely largely on external resources, they are not completely at its mercy.

How Snakes Live

Snakes usually stay out of cold climates. Because the coldest temperature any snake can thrive in is around 65° Farenheit (18° Celsius), snakes normally live in the warmer temperate or tropical zones. There are 4 ways of life for snakes: they can be arboreal (tree-dwelling), fossorial (burrowing), aquatic, or most commonly, terrestrial (they can also be part of each).

Life in the trees

Fully arboreal snakes are usually slender and lightly built. Often they are green to blend into the foliage. Some species can move very quickly through branches, even though the gap is wide and the branch is thin and brittle. Semi-arboreal snakes include the ratsnakes, several kinds of boas and pythons, and green snakes. They do not spend most of their time in trees but seem to climb them because they see prey or need to bask. The reasons that snakes become arboreal are unclear; some think that it is because of better chances for catching prey; others think that it is because the trees may be safer. Whatever the reason or reasons, it can safely be said that snakes have adapted sucessfully to life in the trees.

Terrestrial snakes

The majority of snakes live on the ground. In addition to living terrestrially, a lot of them also live partly in the trees, under ground, or in the water. The body shape of these terra firma snakes varies greatly. There are slender body shapes, like racers or coachwhips, and there are also very heavily built snakes, such as the gaboon viper or blood python. Arid areas, rainforests, grasslands, woodlands, marshes, and mountainous land are the main biomes (habitats), snakes live in. Terrestrial snakes are the most commonly kept, and one of the easiest snakes to own.

Living in the water

Most snakes are capable of swimming fairly well, but some types (aquatic snakes) specialize in the medium. Some of their more obvious adaptations are the placement of their eyes and nostrils higher in the head allowing them to breathe and see without raising their head above water, and the flattening of their tail. The latter is used like a fin, moved side-to-side like a fish to propel themselves. These snakes often prey on fish and other unsuspecting marine animals. All true sea snakes are venomous (though on a surprising note, many sea snakes are quite docile, seldom biting, even when held by divers). These snakes often dive to great depths, staying underwater for long periods of time. Because of their seagoing, unusual habits (not to mention they are fatally venomous), sea snakes are not suitable pets to keep.

Fossorial snakes

Some snakes live completely underground (blindsnakes, wormsnakes), seldom voyaging to the surface. A number of these snakes are completely blind with no eyes and almost no ability to stretch their jaws wide to acommodate large prey. Therefore many are obliged to feed on small creatures. One species in this group holds the record for smallest snake, a thread snake at 4 inches long. Fossorial snakes are probably the most primitive and positively weird snakes.

Where Snakes Live

The Deserts

Snakes seem to be ideally suited to arid areas, as they take most of their fluids from prey and therefore need very little water. The amount of food they need is also minimal. Being ectothermic, snakes need only one-twentieth the amount of food mammals require; they can go many months without food (though this is not recommended!). Most snakes stay in shelters such as burrows during the day, emerging at dusk and retreating when it gets too cold or when morning arrives. Their slender shape allows them to escape the potentially lethal highs and lows in the desert by crawling into crevices and burrows into which other desert-dwellers cannot. Their scales limit water loss, a very important factor in this scorching, water-deprived land. Numerous species have adapted to these arid and semi-arid conditions, including vipers such as rattlesnakes, colubrids like kingsnakes, boids and many others. Reptiles are more common in the desert than most other kinds of animals, being better suited to this barren lifestyle. Snakes are one of the most successful desert animals.

Tropical Forests

Tropical forests are well known for their diversity in flora and fauna. Rainforests are one of the most ideal habitats for snakes; temperature is seldom a problem, as it is always warm near the equator, the humidity is high, and water is abundant. They have a wide range of microhabitats such as terrestrial, arboreal, fossorial, and aquatic. Places to hide abound in the rainforest since the vegetation is thick; food is abundant, so snakes can be selective to what they want to eat. Contrary to popular belief, the number of snakes to each species are suprisingly low in the rainforests. In a study conducted, it was found that the diversity was high, but the numbers of individual species were low; of the fifteen families recognized, all were found except the families boyleridae and acrochordidae.

Temperate Forests

In contrast to tropical forests, temperate forests are not rich in snakes, neither in species nor in numbers. The cool climate of temperate regions is compounded by the canopy cover and such species that are found in this habitat are usually restricted to lightly wooded areas, forest fringes, and clearings. Due to agricultural practices, the temperate forests are decreasing, leading to a reduction in numbers of snakes.

Swamps and Marshes

Swamps and marshes may be found where the water table is close to the surface. They may be permanent or seasonal, tropical or temperate. Watersnakes (genus Nerodia) and gartersnakes (genus Thamnophis) are some kinds of snakes that live on the fringes of ponds, lakes, and creeks, feeding on fishes and amphibians. Some inhabit semi-saltwater mangrove forests where the climate is warm and the food is plentiful. Semi-aquatic areas usually have an abundance of food as the water attracts numerous animals. Snakes seem to have taken good advantage of the swamps and marshes.

Savannahs and Grasslands

Grasslands range throughout the middle latitudes covering about 1/4 of the world's surface. The grasslands are known locally under such names as prairie (in North America), savannah (in Africa), and steppe (in Asia). This habitat seems to have never been fully inhabited by snakes, as there is little cover, making it easy to be spotted by predators. Overall temperatures may be too low in many of these areas and food supply sparse. However, several snakes have adapted to living in grasslands: a few Pythons, some Colubrids such as Western Hognose snakes (Heterodon nascius) and Bullsnakes (Pitouphis sayi), some Elapids, and a few Rattlesnakes, though none of these snakes are restricted solely to savannahs.

Aquatic Habitats

Only a few specialized species are totally at home in the water. Completely aquatic snakes such as sea kraits (Laticaudidae) and sea snakes (Hydropheidae) are limited to the tropics zone because the water temperature has to be close to their comfort level. All sea snakes are fatally venomous and that is how they catch their food. Most aquatic snakes mainly feed on fish, though some also eat eggs, shrimp and other invertebrates. This is another habitat that is not widely used when it comes to snakes.