Information about basic types of movement, speed, feeding and hunting habits of snakes. What are the defenses of snakes.
In general, snakes behave in the same ways as other animals do. They must find their food and mates, expose their bodies to the proper amounts of heat to maintain their temperature, and escape from their enemies.
Exactly how a legless animal can move with so little apparent effort and in what appears to be a swift manner has long been a puzzle to man. It was once thought that a snake “walked on its ribs”—that is, that a snake moved its curved ribs, which stick out from the backbone, back and forth like so many legs. However, X-ray motion pictures of snakes have shown that the ribs do not move at all but merely act as the base attachments for muscles that pull the broad plates on the belly, called ventrals, back and forth. Since the plates overlap like the shingles on a roof, their backward-projecting edges catch on rough ground and help to push the body of a snake forward. This is one basic method by which snakes move. However, snakes have at least four different ways of movement, and while the different methods are characteristic of certain snakes, many snakes can use all of the methods, and they often use two or more in combination.
Basic Types of Movement.
Most of the common snakes of field and woodland use a method of lateral undulations to move along. In this method, the snake lays out its long body -in a series of S-shaped curves that hug the ground. By pressing backward and outward against the rough ground surface, the snake is pushed forward on its glass-slick ventrals, or belly scutes. Lateral pressure to produce forward movement is somewhat like “squirting” a slick prune seed through your fingers by pressing it on the sides. This method of movement works best for snakes of moderate size and bulk. It is difficult for a very large or very heavy snake to find strong enough irregularities on the ground to press against. All snakes, however, use essentially this system to swim.
Heavy-bodied snakes, such as vipers and large pythons, often use a rectilinear method, of movement. This method, sometimes known as caterpillar motion, relies on the belly scutes and their associated muscles. Small groups of the belly scutes of a section of the body are pulled forward, while the backward-projecting edges of other belly scutes catch on the ground and keep the snake’s body from slipping back. These scutes that hold still are then pulled forward, while the previously moved scutes hold still. By using this method of alternately moving certain belly scutes and holding others still, the snake can travel forward in a straight line. Although no great speed can be attained, the snake’s body seems to flow forward as though pulled by a string.
Perhaps the most unusual and agile method of movement practiced by snakes is the process called sidewinding. This method is used mainly by desert vipers that live on sand so fine that it would make ineffective the other methods of movement that depend on resistance to the backward push. In sidewinding, the snake presses the rear part of its body down while it throws a loop of its forebody to one side and holds its midbody clear of the sand. The snake then transfers its weight from the rear section to the front, while throwing out another coil. Thus a snake faces in one direction and moves at an angle to it in a bewildering rolling movement. This strange way of progression allows the snake to move swiftly across fine sand. At the same time, it keeps much of its body off the substratum. Both of these features can be advantageous if the sand is hot.
A fourth method of moving is the concertina climbing used by certain tree boas. A long body and good muscles are essential for this movement. To climb a smooth vertical trunk, such as a stalk of bamboo, the snake first wraps itself around the trunk near the base. It then reaches far up the trunk and hooks its neck around it. More of the body is pulled up to make a firm coil. Then the rear coil is loosened and pulled up to join the rest of the body. A firm grip is taken by the rear part of the body in this new position, and the process is repeated. Only a few snakes are able to climb in this fashion. Most tree snakes depend on irregularities in the trunk of the tree and wedge their belly scutes into these irregularities and climb up slowly by a combination of lateral undulation and rectilinear methods until they get to the branches.
The black snake that glides across the path and the grass snake that disappears under a bush look as if they are traveling at a high rate of speed. However, this is a visual impression that is produced by the sleek form and smooth movements of the snakes. Actually, compared with many other animals, snakes move very slowly. A rattlesnake (Crotalus species), for example, may crawl at a rate of 2 miles (3.2 km) per hour if it is in a hurry. The sidewinder (Crotalus cerastes), with its peculiar mode of travel, is the fastest of the rattlesnakes and may attain a speed of 3 miles (4.8 km) per hour.
The European grass snake (Natrix natrix) has been judged to move 4 miles (6.4 km) per hour when pressed, and the coachwhip (Mastico-phis flagellum), certainly one of the fastest snakes in North America, has been calculated to dash at a speed of a little over 5 miles (8 km) per hour. The record for speed is thought to be held by the African mambas (Dendroaspis species). A teased mamba chased a man at a clocked speed of 7 miles (11.2 km) per hour. A man can run at well over twice that speed, however.
All snakes eat some kind of animal for their food. Not only do they eat other animals, but they always eat them whole. A snake’s jaws and teeth are not fashioned in ways that would allow the snake to chew food or even to tear it apart as crocodiles do.
Though restricted to animal foods, snakes do not seem to be restricted in any other way. Animals ranging in size from ants to deer are eaten by various snakes, though most snakes are very specific about the kind of animal that they will eat. Furthermore, they can swallow much larger prey than might be expected. Due to the construction of the snake’s jaws, a small garter snake (Thamnophis species) can swallow a sizable frog, and a modest sized python can swallow a 40-pound (18-kg) pig.
Both the typical blind snakes (family Typhlopidae) and the slender blind snakes (family Leptotyphlopidae) feed mainly on ants and termites. The snakes often live in the nests of the insects, apparently protected from the bites of insects by their hard glossy scales. Some snakes (Dipsas) feed entirely on snails and have lower jaws and teeth that are specially constructed to pull these soft-fleshed animals from their shells. The red-bellied snake (Storeria occipitomaculata) of North America feeds almost exclusively on slugs, while its close relative the brown snake (S. dekayi) is satisfied with a diet of earthworms.
Many of the tropical tree snakes feed on lizards, as does the ground-dwelling long-nosed snake (Rhinocheilus leconti) of the American Southwest. Racers, such as the black racer (Coluber constrictor) of North America, accept both mice and frogs as food, and the American garter snakes will eat any animal they can capture and overcome. The cottonmouth (Agkistrodon piscivorus), the copperhead (A. contortrix), and the massassauga (Sistrurus catenatus) will take either cold-blooded or warm-blooded prey. However, most other snakes, including most rattlesnakes, are much more restricted in their diets.
Most water snakes refuse all but cold-blooded animals. The common water snake (Natrix sipedon) of North America feeds mainly on fishes and frogs, as do most of its close relatives. Other American water snakes (Regina species), however, feed mostly on crayfish, and an Indo-Australian rear-fanged water snake (Fordonia) is known to feed on fiddler crabs.
Most of the larger snakes feed on birds and mammals. Diamondback rattlesnakes (several Crotalus species) feed on cottontail rabbits and squirrels. Boas and pythons feed on mammals of appropriate size. The record meal that has been reported appears to be that of a 16-foot (4.8-meter) African rock python (Python sebae) that swallowed an impala weighing 130 pounds (59 kg).
Snakes are very irregular feeders even when food is readily available. A large python may take only seven or eight meals in a year, while smaller snakes commonly eat every week or ten days. Except when they are hungry or during the mating season, snakes tend to remain in one place and move only enough to adjust their body temperature to the preferred level.
Once they feel the pangs of hunger, snakes may travel over a great expanse of territory and expend considerable energy to find their next meal. A fox snake (Elaphe vulpina) was once observed crossing a field, encountering a small tree, climbing it, searching all its branches for a bird or nest, and then continuing on across the field in search of food. This kind of thorough search is typical of the hunting behavior of snakes.
Most snakes select prey animals that are so small or so innocuous that the snake needs no special adaptation to secure it. The snake merely grasps the prey animal with its mouth, orients it so that it will slide dov«n the gullet with the least difficulty, and then swallows it. This procedure is characteristic of most water snakes, American garter snakes, racers, and many other species.
Some snakes, however, feed on prey that can escape readily or that can bite or defend themselves in some way. Many snakes that feed on mice or rats, such as the rat snakes (several genera, including Elaphe and Ptyas), bull snakes (Pituophis), and king snakes (Lampropeltis), have evolved methods of killing the prey quickly by constriction. The same is true of boas and pythons that feed on larger prey. These snakes throw two or three coils around the body of the prey animal, and constrict its chest. Each time the stricken prey exhales, the attacking snake “takes up the slack.” In these cases, the prey ordinarily dies from suffocation or from interference with heart action. Bones are only rarely broken, and the prey is never reduced to a pulp, as folklore would suggest.
The lizard-eating tree snakes and some others have evolved venoms that paralyze the prey animal quickly, or cause its death. The boomslang and the bird snake of Africa have developed venoms strong enough to capture the large and tenacious chameleons of that continent. Other venomous snakes have also developed extremely potent venoms that can subdue their prey and that can also be used for the snake’s defense against other larger animals, including man. The venoms of various snakes appear to kill the snake’s usual prey especially rapidly, although they may also De effective against other animals as well.
In North America, skunks, opossums, and pigs are among the mammals that commonly prey on snakes. In Africa and Asia, the mongooses and civet cats are common predators. Birds are also among the general and foremost enemies of snakes. The secretary bird of Africa is well known to feed on snakes. Even the lowly chicken will eat small snakes, including venomous ones, and wild turkeys in North America are reported to attack rattlesnakes without provocation. Many hawks feed on snakes to some extent, and the broad-winged buzzard hawks feed on them extensively, often including snakeskins in the construction of their nests.
However, some of the greatest enemies of snakes are other species of snakes. Racers of all kinds are apt to pick up smaller snakes that come their way, and each continent has at least one species of snake that feeds almost entirely on other snakes. The members of the cobra family are well-known snake-eaters, and the king cobra (Ophiophagus) seldom takes any other food. The coral snakes (Micrurus) of the Americas feed on lizards and occasionally on fishes, but mainly on other snakes. This is also true of the Indian kraits (Bungarus specie?).
Protective Coloration and Hiding
Most snakes rely for protection on their coloration, which is often a close match of that of their surroundings. Desert-dwelling snakes, for example, are ordinarily pale and sand-colored, while forest-living species often resemble leaves in color and pattern. Many tree snakes, for example, have elongate vinelike bodies colored to match their surroundings.
Among snakes that are active during the day, only a few comparatively swift-moving kinds are solid-colored. Some are striped to give an appearance of speedier movement. Many secretive venomous snakes, seem to have “warning colors” to warn possible predators of their dangerous nature.
On the other hand, nocturnal or burrowing snakes can be almost any color or pattern without advertising their presence to other animals. Most nocturnal snakes hide under rocks or logs during the day, and many snakes, including blind snakes, have evolved burrowing habits to hide themselves.
When actually menaced by a predator in close proximity, a snake may suddenly change its behavior. The cobra or mamba that has been attempting to disappear may suddenly face its aggressor and spread out the loose skin of its neck region in a so-called “warning hood.” It may then strike out at the enemy. A spitting cobra may squirt venom into the eyes of a threatening animal, A rattlesnake may warn of an impending attack with a characteristic raspy rattle, and many vipers that have no other means of making noise hiss loudly if disturbed, as do some nonvenomous snakes.
To threaten possible predators, some of the bush snakes (Leptophis species) and vine snakes (Oxybelis) open their mouths, which are brightly and contrastingly colored, but these snakes usually refuse to bite. The North American cotton-mouth also threatens in this way, but its threat is far from empty, for if further provoked it will bite. In fact, most snakes, whether venomous or nonvenomous, will bite if cornered or strongly threatened.