(3) Tree Snakes include both venomous and innocent genera. They are none of them large, many of them of a brilliant green, and some of them exquisitely beautiful. Slender and active, the harmless kinds skim among the branches, which scarcely bend beneath their weight. Many of them have small and peculiarly arranged ventral shields, not requiring to hold on in progression; many also have long prehensile tails, which wind and cling while the little acrobats swing to and fro, or hang down to take a young bird or an egg out of the nest. The poisonous kinds of tree snakes abound in India, have a thick body, broad head, and a dull, sluggish habit, but still are handsome as to colour, and mostly green. They hide in the trunks of trees, or in the hollow forks of the branches, and rarely venture upon the ground. Some, however, live only in bushy foliage lower down, while other arboreal species frequent the highest branches, where, moving with amazing celerity, they are as much at home as the feathered inhabitants.
(4) Fresh-Water Snakes are especially adapted for an aquatic existence, and have their nostrils on the top of the snout, to enable them to breathe easily when in the water. Some of them can hold on to weeds or other things by their tails. They swim and dive, and are as active as eels. None are very large, and all are harmless. But a good many of the second group that are poisonous, spend so much of their time in the water that they are known as ‘water vipers,’ ‘water moccasins,’ etc., though not truly water snakes.
(5) Sea Snakes.—All highly venomous. These, as also the fresh-water snakes, are treated fully in chapters xiii. and xiv. The five divisions assist the student towards grasping an idea of the principal groups, but the whole five pass into each other by intermediate forms and imperceptible degrees.
Some other general characteristics of the Ophidia are that all are carnivorous, catching their prey alive; all are oviparous; and in organization and intelligence they rank between birds and fishes,—higher than fishes in having lungs, and lower than birds, which are warm-blooded animals. Their heart is so formed as to send only a portion of blood to the lungs on each contraction of it; their temperature, therefore, is that of the surrounding atmosphere (see p. 142). Their normal condition, particularly that of the venomous species, is one of lethargic repose and indolence, with a disposition to retreat and hide, rather than to obtrude themselves. On this account, and also because so many of them are nocturnal in their habits, less has been truly known of serpents than of most other creatures, prejudice having added to a prevailing indifference regarding them. The duration of their lives is uncertain, or whether they have a stated period of growth. Some naturalists think they grow all their lives; but this must not be taken literally, or that if a small snake happened to escape dangers, and live a very long while, it would acquire the dimensions of a python. Some think that formerly the constrictors did attain more formidable proportions than those of the present day.
Snakes have small brains, slight intelligence, and slow sensations, amounting almost to insensibility to pain. They can live a long while without their brains and without their heart; while the latter, if taken from the body, will continue its pulsations for a considerable time. Also if the head be severed, the body will for a certain time continue to move, coil, and even spring, and the head will try to bite, and the tongue dart out as in life.
Persons who dislike snakes continually ask, ‘What is the use of them?’ That they are not without a use will, I hope, appear in the course of this work, were it necessary to preach that all things have their use. But in one habit that offended Lord Bacon, viz. of ‘going on their belly,’ lies one of their greatest uses, because that, together with their internal conformation and external covering, enables them to penetrate where no larger carnivorous animal could venture, into dense and noisome morasses, bogs, jungles, swamps, amid the tangled vegetation of the tropics, where swarms of the lesser reptiles, on which so many of them feed, would otherwise outbalance the harmony of nature, die, and produce pestilences. Wondrously and exquisitely constructed for their habitat, they are able to exist where the higher animals could not; and while they help to clear those inaccessible places of the lesser vermin, they themselves supply food for a number of the smaller mammalia, which, with many carnivorous birds, devour vast numbers of young snakes. The hedgehog, weasel, ichneumon, rat, peccary, badger, hog, goat, and an immense number of birds keep snakes within due limits, while the latter perform their part among the grain-devouring and herbivorous lesser creatures. Thus beautifully is the balance of nature maintained.
Dr. Kirtland, an eminent naturalist of Ohio, who lived at a time when that State was being very rapidly settled, namely, during the early and middle part of the present century, observed a great increase of certain snakes as game birds which fed on them decreased. The latter were, of course, in request for the market, and the snakes, the ‘black snake’ particularly, having fewer enemies to consume him, flourished accordingly. It would be worth while to ascertain whether the farmer in Ohio had reason to rejoice over this redundancy of rat and vermin consumers. At the present time, when so much of the land is under cultivation, snakes have decreased again through human agency.
