Serpents travel on their bellies, moving their bodies in lateral undulations, and often running with amazing swiftness. Every pair of ribs is connected at their lower ends with one of the large abdominal scales, or "scutes," and it is generally believed that the creature moves by the pressure and pushing of these scutes and rib points on the ground; but Boulenger, a leading authority, thinks that their importance has been somewhat exaggerated, although of undoubted use for the purpose of climbing, at which some species are remarkably adept.
Some snakes lay eggs with a tough, parchmentlike shell; others retain them within the body until the young are fully developed.
Snakes do not migrate nor wander far from their birthplace in search of food. Desert dwellers burrow under the sand for protection from the heat, and go abroad at night, as is the habit of many snakes. In the colder climates the serpents hibernate, collecting in companies tangled together like a ball in some animal's burrow, or in a den among the rocks, the hardier ones occasionally appearing on warm days in winter. When they come out in spring they are likely to make their way to wet lowlands, in search of frogs, toads and mice.
The order is divided into nine families, which will now be considered in the order arranged by G. A. Boulenger of the Zoölogical Society of London. The first four families are small, wormlike, burrowing creatures, with a large number of species distributed in warm countries throughout the world, and regarded as relics of an ancient type. The beautiful coral snake of South America, which grows to a yard in length and is only partly subterranean in habit, leads from these to the great family of boas and pythons (Boidæ) which contains the biggest serpents that exist, or so far as we know, ever have existed. The members of this family have vestiges of pelvis and hind limbs, appearing externally as clawlike spurs. The Boidæ comprise sixty or seventy species and the range of the family is world-wide. They mostly prefer wooded districts, climbing trees, assisted by the short and partly prehensile tail. Some are semiaquatic. All are rapacious, and feed by preference on warm-blooded creatures.
The family is divided into two subfamilies, Pythoninæ and Boinæ, but the difference between them is confined mainly to certain bones in the skull. The pythons belong entirely to the tropics of the Old World, except a single species in southern Mexico; and number about twenty species. The Boinæ are chiefly American. None is venomous.
A famous python is the six-foot, tree-dwelling carpet snake of Australia, black, beautifully marked with a pattern of yellow dots. A very large species is the reticulated python of Indo-China and the Malayan region, having an arrangement of dark lozenges on a lighter ground. India has a similar species, reaching a length of thirty feet, marked with reddish brown patches on a yellowish ground. This (Python molurus) is the one most often seen in zoölogical collections on account of its hardiness; but it is a savage creature, almost untamable. Like others of these big serpents it is able to make very long fasts; indeed their life, in this respect, seems to consist of gorges, followed by long periods—sometimes several months—of fasting and repose, entirely voluntary. It appears from observation of captive specimens that they have individual preferences for a certain kind of food, and perhaps wait for it; thus one in the Jardin des Plantes, Paris, refused various toothsome animals for months until a goose was offered, which it seized hungrily, and then sulked through long weeks until another goose was given.
Africa has two pythons, one (P. regius) confined to West Africa, the other (P. sebæ), common from the Sudan to the Cape. "The latter," William C. Scully says, "is the largest of African snakes, occasionally attaining a length of more than twenty feet, with a circumference of eighteen inches. One is recorded of twenty-five feet. It principally frequents rocky chasms in moist, warm forests. It is not dangerous to man, being quite nonvenomous, but it will fight fiercely if attacked, and the long, sharp, teeth may inflict a severe bite. The python usually preys upon small animals, such as minor antelopes, monkeys, conies, and birds. Sometimes this snake coils itself at the bottom of a stream and lies with its nose just emerging. When a small buck comes to drink, the snake seizes it by the nose, the recurved teeth taking an inextricable grip. After the buck has been drowned the python coils itself around the body and crushes it for convenience in the process of swallowing.... The python does not regard the horns, which sometimes may be seen sticking out through the abdomen. These wounds quickly heal, the snake apparently being none the worse for the perforations.
"So far as I know the python is the only snake which incubates its eggs. Such, numbering from thirty to fifty at a brood, and weighing about five and a half ounces each, are usually laid in a deep rock crevice or in the deserted burrow of an ant bear or hyena. The mother coils herself over and around them."
Let us turn now to the boas. Popularly the whole tribe is frequently spoken of as "boa constrictors," but that is the scientific name of only one among several species, the Boa constrictor of the West Indies and tropical South America. It is the one most common and best known, and, as it is easily tamed, is the one often seen in the hands of performers with serpents in circuses, and exhibited in menageries. In many places in South America the natives, according to Leo Miller, keep them running at large about their huts to catch rats. In forested regions they spend most of their time in trees, but in an open country lie about on the ground, retreating when alarmed into some hole, as of a viscacha—their favorite prey on the plains.