Admitting it to be a dubious creature, with neither name nor ancestry in ophidian annals, I must not give it precedence of the recognised water snakes; but it shall figure in the heart of my book notwithstanding.
‘Fresh-water snakes’ form the fourth, and ‘Sea snakes’ the fifth of the five groups into which Dr. Günther has separated the ophidian families; but the gradations between the land and the fresh-water species, and between the latter and the salt-water snakes or the true Hydrophidæ, are, like all other herpetological features, extremely close. There are water-loving land snakes and land-frequenting water snakes, that is, those which are equally at home in both. In the true water species, however, we find modifications of ordinary rules which show them to be peculiarly protected and adapted for an aquatic existence.
One notable characteristic in all, both salt-water and fresh, is the position of the nostrils on the top of the snout, and in many these are protected by a valve which closes at will. As air-breathing animals they must come to the surface, but the timid, stealthy ophidian instinct which seeks to hide from observation can be indulged even in the water, with the nostrils so situated that only a very small surface of the head need be exposed. Could we examine the interior of the mouth we should doubtless find some slight variation in the position of the glottis also. In a foregoing chapter we saw that the trachea opens exactly opposite to and close behind what Dumeril calls the ‘arrière-narines;’ ‘leur glotte qui est à deux lèvres et qui represente un larynx très simple, s’ouvre dans la bouche derrière le fourreau de la langue ... elle s’élève pour se presenter dilatée sous les arrière-narines.’[71] The glottis of water snakes must have a still more upward direction to present itself to those air passages. Perhaps water snakes do not require to yawn so frequently as is the habit of their terrestrial relatives; and if they do, it must be a rare privilege to be able to inspect the process, as one can so frequently do with the pythons and vipers at home. Our authorities do not give us much information on this point.[72]
Their moderately long tapering tail is used as a propelling power. Exteriorly, too, water snakes have smooth non-imbricated scales, though exceptions exist in those species which frequent both land and water, as the Tropidonoti, a large family of which our common English ring snake is a member, and which, as their name denotes, have all keeled scales, from τρόπις, τρόπιδος, a keel. These, also, can elevate their ribs, and so flatten the body in the water, another assistant in swimming.
A marked exception to the smooth-scaled, water-loving snakes is the African viper, known as the ‘River Jack’ from its partiality to water. Vipera rhinosceros, from the spinous scales which have the appearance of horns on its nose, is allied to those described in the 18th chapter. Though not strictly a water snake, it much frequents it, and glides through it with ease, the more remarkable because, in common with those other ‘horned vipers’ of Africa, it has a short, insignificant little tail, which can be of little use as a propelling power. Altogether, it is one of the ugliest and most ferocious-looking of the whole serpent tribe, with a thick, heavy body, a dingy, rough exterior, and strongly-carinated scales. Excepting in colour, and a more horizontal inclination of its horns, it is not unlike the V. nasicornis of the coloured illustration, chap. xviii.
While all the Homalopsidæ or true fresh-water snakes are innocent, there are many other venomous kinds known as ‘water serpents,’ both in Africa and America. For example, the ‘water viper,’ or ‘water moccasin,’ Cenchris piscivorus, whose aquatic and fish-eating propensities were described in the chapter on Tails. This ‘thorn-tail’ viper has not, however, the nostrils of the true fresh-water snakes or Homalopsidæ. In Australia also are several poisonous species, known vernacularly as ‘water snakes;’ but strictly speaking, and on the authority of Günther, the true Homalopsidæ are all non-venomous.
To describe these more minutely from Günther, Krefft, and Dr. E. Nicholson, ‘they have a body moderately cylindrical, a tail somewhat compressed at the root, and more or less prehensile. Many of them have a distinctly prehensile tail, by which they hold on to projecting objects;’ and in times of storms and strong currents we can imagine the importance of this security to them. Their eyes, though prominent, are small, and thus less exposed to injury; and the nostrils, as already stated, are on the upper surface of the head, and provided with a valvule. Another peculiarity is that the last or back tooth of the maxillary bone is a grooved fang, a transitional tooth between an ordinary one and a fang; but there is no evidence of any poisonous saliva connected with it. Indeed, as we may repeat, Dr. Günther distinctly affirms that all the fresh-water snakes are harmless and thoroughly aquatic, though a few are occasionally found on the beach. They inhabit rivers and estuaries, feeding on fish, and rarely coming to land; some of them frequent brackish waters, and even enter the sea. These latter in their organization approach the true marine serpents. One Indian example, Hydrinus, is semi-pelagic. They are all viviparous, producing their young in the water; and they belong to the tropical or semi-tropical regions. In Australia they are found only in the far north; but in America some so-called ‘water snakes,’ which spend most of their time in the water, frequent rivers which are frozen over in winter, during which season they probably undergo hibernation in holes near the banks.
Several of the older naturalists describe ‘water snakes’ in words which leave us no doubt as to the numbers, though of their name we cannot be so certain. Carver in 1796 mentioned some small islands near the western end of Lake Erie, so infested with snakes that it was dangerous to land upon them. It is impossible that any place can produce a greater number of all kinds of snakes, particularly the ‘water snake,’ than this. He says: ‘The lake is covered near the banks of the islands with the large pond lily, the leaves of which lie on the surface of the water so thick as to cover it entirely for many acres together, and on each of these lay wreaths of water snakes, amounting to myriads, basking in the sun.’ A sight of the last century this. I have passed over that part of Lake Erie and through the Detroit river, and remember the islands and the water-lilies and other attractive objects, but ‘wreaths of water snakes’ were not of these.
Lawson, too, can assure us of their habitat, but not their name, and his account is of worth chiefly to verify their swarming numbers. It is possible that some of those which he describes are now extinct or very rare. ‘Of water Snakes there are four sorts. The first is of the Horn Snake’s Colour, though less.’ (This might be the young of the ‘water moccasin,’ Cenchris, or Trigonoceph. piscivorus.) ‘The next is a very long Snake, differing in Colour, and will make nothing to swim over a River a League wide. They hang upon Birches and other Trees by the Water Side. I had the Fortune once to have one of them leap into my Boat as I was going up a narrow River. The Boat was full of Mats, which I was glad to take out and so get rid of him. They are reckoned poisonous. A third is much of an English Adder Colour, but always frequents the Salts, and lies under the drift Seaweed, where they are in Abundance, and are accounted mischievous when they bite. The last is of a sooty, black Colour, and frequents Ponds and Ditches. What his Qualities are, I cannot tell.’
Catesby is responsible for having called Tropidonotus fasciatus ‘the brown water viper,’ a stumbling-block to many ever since, much confusion existing between this and the true ‘water viper,’ the dangerous moccasin snake. Occasionally they are very dark. They are rather thick and viperish-looking as well, but are perfectly harmless.