Snake Reptiles

Snake Reptiles Internally, they have lost the urinary bladder. Certain burrowing lizards may have only front or hind limbs or be completely legless. The visceral organs are elongated, with reduction of the left member in relation to the right; the left lung is greatly reduced or even lost entirely. However, snakes possess increased numbers of vertebrae and have developed two novelties among vertebrates: a tracheal lung in the neck region and a venom-conducting system for subduing prey. Unlike lizards, snakes lack movable eyelids, which results in a continuous and often disconcerting stare. Classified with lizards in the order Squamata, snakes represent a lizard that, over the course of evolution, has undergone structural reduction, simplification, and loss as well as specialization. Snakes also lack external ear openings. All snakes lack external limbs, but not all legless reptiles are snakes. snake, (suborder Serpentes), also called serpent, any of more than 3,400 species of reptiles distinguished by their limbless condition and greatly elongated body and tail.

Snakes are thought to have evolved from terrestrial lizards as early as the Middle Jurassic Epoch (174.1 million to 163.5 million years ago). Only a small percentage (fewer than 300 species) are venomous, and of those only about half are capable of inflicting a lethal bite. The oldest known fossil snake, Eophis underwoodi, was a small snake that lived in southern England about 167 million years ago. Snakes and humans Snakes are misunderstood and often maligned, primarily out of ignorance about their true nature and position in the natural world. Although snakebite mortality worldwide is estimated at 80,000–140,000 people per year, the majority of deaths occur in Southeast Asia, principally because of poor medical treatment, malnutrition of victims, and a large number of venomous species. Although there are about 8,000 venomous snakebites per year in the United States, the average number of annual fatalities is less than 10 or so per year—fewer than are attributed to bee stings and lightning strikes. In Mexico, 10 times as many people die annually from bee stings as from snakebites. All snakes are predators, but venomous snakes (that is, biting snakes that use their fangs to inject toxins into their victims) have given an inaccurate reputation to the entire group, as most people cannot tell the dangerous from the harmless. Rattlesnakes, for example, are venomous, and large ones are quite dangerous owing to the amount of venom they can inject. In either case, the snake is only defending itself. Statistics show that the vast majority of snakebites occur while either catching and handling captive snakes or trying to molest or kill wild ones. Snakes can control the amount of venom they inject and may bite aggressively for food or defensively for protection. When approached or molested, they will coil up and rattle as a warning to be left alone, striking only as a last resort. Snakes have a limited amount of venom available at any given time and do not want to waste it on nonprey organisms. As a result, about 40 percent of bites suffered by humans are defensive in nature and “dry” (without envenomation). Nevertheless, snakes are inoffensive under the vast majority of circumstances. Very few snakes are truly poisonous. However, most are shy and retreating, and none will attack a person unmolested. It is interesting to note that, although most people profess to fear or hate snakes, one of the most visited areas of any zoo is the snake house—proof that snakes are mysterious and fascinating, even if they are loathed. One of the most common, yet harmless, poisonous snakes in North America is the garter snake (Thamnophis), whose body has the ability to absorb and store the toxins of the newts, salamanders, and other poisonous prey it eats. Even in these scenarios, only two snakes have a reputation as dangerous aggressors: the black mamba (Dendroaspis polylepis) of Africa and the king cobra (Ophiophagus hannah) of Southeast Asia. Most cases of reputed snake attack are based upon encroachment by a person into the snake’s territory, which makes it feel trapped or cornered, or provocation of a snake during the breeding season. People are rarely indifferent about them, generally exhibiting emotions that range from religious awe and superstitious dread to repulsion and uncontrollable fear. Given their exquisite colours, patterns, and graceful movements as they crawl, swim, or climb, some snakes can be considered among the most beautiful animals.

In common parlance, venomous snakes are often referred to as “poisonous snakes.” This phrase is not technically correct, because the term “poisonous” only applies to organisms that unload their toxins when another organism consumes them.Nearly every culture since prehistoric times (including various present-day cultures) has worshipped, revered, or feared snakes. Although Satan is depicted as a serpent in the biblical account of the Creation, snakes are revered by most societies. Many stem from the snakes’ biological peculiarities: their ability to shed their skin is associated with immortality; their ever-open eyes represent omniscience; their propensity for sudden appearance and disappearance allies snakes with magic and ghosts; a phallic resemblance embodies procreative powers; and the ability to kill with a single bite engenders fear of any snakelike creature. A vast global compendium of superstitions and mythologies about snakes has sprung up. Serpent worship is one of the earliest forms of veneration, with some carvings dating to 10,000 BCE.The removal of such enormous numbers from the wild threatens the survival of these species, and many snake populations are in decline as a result of capture and habitat destruction. Hundreds of thousands of live snakes are collected for sale in the international pet trade. The hides of six snake species (especially pythonss and wart snakes) are commonly bought and sold in the skin trade. Nearly 100,000 ball pythons and 30,000 boa constrictors are imported annually into the United States. The release of nonnative pet snakes into the wild has also led to the introduction of several invasive species, including the Burmese pythons that have devastated small mammal populations in the Florida Everglades. The number of rattlesnakes used for their skins is minor in comparison.It is likely that snakes, like sea turtles, can migrate by using celestial or geomagnetic cues. Except for these few weak instances, there is no development of social behaviour in snake populations—no establishment of social hierarchies, no territoriality, and perhaps no dominance. At such times, snakes may enter a short period of dormancy, which is at least in part a consequence of the effect that the dry season has upon their prey. No matter where they live, snakes are subjected to pressures from the living (biotic) parts of the environment as well as from the physical, nonliving (abiotic) parts. Hiding places and basking sites are occasionally shared; this again is a consequence of availability, and in the tropics, where hiding places abound, it is rare to find more than one snake at a time under a log or a rock. While combat dance (see below) certainly establishes a dominant individual temporarily, there is no indication that awareness of this dominance is retained by either snake. Most snakes do not spend much of their time doing anything but resting. The stimuli are felt by all almost simultaneously, and snakes emerge by the dozens or even by the hundreds from some denning places. But the amount or degree of challenge to the snake from different segments of the environment changes drastically depending upon the region it inhabits. Many of the changes that occur in the individual snake after arriving at the hibernaculum are direct results of its dependence upon the environment. Hunting of food is strictly an individual act for snakes; there are no known instances of cooperative hunting, as seen in some mammal and bird species. A snake’s primary activity is concerned with either thermoregulation or finding live food, which often involves passive waiting rather than active searching. Sea snakes (subfamily Hydrophiinae) differ in this respect, sometimes being seen traveling in large troops, which seems to indicate an urge to aggregate. As the body cools, the heartbeat and respiration slow almost to a stop, and there is no muscular activity, little digestion, and no defecation. Fertilization of the egg can take place immediately after copulation, but, in at least some species, the female can store the sperm for several years, using them to fertilize successive batches of eggs. Interactions between individuals Snakes in both tropical and temperate regions tend to be solitary in their habits. There is some tendency for females of certain species in temperate areas to use a single site for egg deposition. The thermoregulation problem varies with latitude and altitude. The only break in the rhythm comes in the dry season—and this only when the dry season is not just a period of slightly less rainfall. An individual living in the hot, humid tropics of Africa, with comparatively constant temperatures close to optimum throughout the year and ample moisture from both rainfall and the surroundings, faces environmental problems that are overwhelmingly biotic, involving competition with other members of its own species for food, the challenge from other species of snakes and perhaps other vertebrates for possession of the ecological niche, and constant pressure of the predators that find it a tasty morsel. The denning and mating aggregations are, for the most part, the only social events of the season. In such a case, the snake simply dies. At the end of the cold season, the snake is totally dependent upon the changes in its surroundings to bring it back to activity; it cannot rouse itself. At higher latitudes and altitudes, during periods of maximum stress (which for most snakes are the cold months), the animals must seek out a place where they can be completely inactive and nonreactive, where their inability to respond to the stimulus of danger is compensated for by the absence of danger, and where the surrounding extremes of low temperature and low humidity remain within tolerable limits. Scent trails, most commonly laid down by females during the breeding season, are also used. The actions and reactions of a snake in temperate North America are distinct from those of one living in the American tropical lowlands but are similar to those of another living at higher altitudes in the Andes of Ecuador. A dominance that must be reestablished at every encounter does not contribute to a social structure. This dormant period is similar to hibernation in winter by temperate-area snakes, although little is known about physiological changes that may or may not take place in tropical dormancy. These differences between animals from different parts of the world are reflected in their life histories, and it is neither possible nor legitimate to speak of the “life history of the snake” unless one speaks of only a single region or species. Dormant periods In the tropics, life continues at approximately the same activity level throughout the year. Such places are few and far between, and good hibernacula (dens used for hibernation) are recognized over generations and are utilized year after year, with snakes of several different species often sharing a den. However, its survival is challenged continually by its physical environment, and death from overheating, freezing, or dehydration is a repetitive threat. Female sea snakes also congregate in large numbers in seawall caves at parturition time, but this may have no social significance, since it seems to be a consequence of availability of a safe place for the young to be born rather than aggregational behaviour per se. Physiological changes that are not correlated with or responsive to the surroundings also take place, but not to a degree comparable to those occurring in a hibernating mammal, and there is no “alarm system” to stir the snake into activity if a tolerance limit is passed. On the other hand, the common adder, or European viper (Vipera berus), living north of the Arctic Circle in Europe, is the only snake present in the area and lives practically unchallenged in its niche. In some species, copulation takes place immediately after enough of the sun’s rays have been absorbed to permit the development of an interest in the surroundings; in others, copulation is the final act before entering hibernation, and the sperm remain dormant in the hibernating female.