In the slough of a rattlesnake you may see the form of this pit. It is lined with scales, and reversed in sloughing, perfectly shaped as a tiny glove finger.
When Dr. J. E. Gray, F.R.S., etc., edited a short-lived little magazine in 1831 called the Zoological Miscellany, the whole of the known Crotalidæ consisted of ten genera and thirty species, of which sixteen species belonged to Asia and its adjacent islands, one to South Africa, and the rest to America. When he published his catalogue of snakes belonging to the British Museum in 1849, he enumerated eleven genera and thirty-seven species. Wallace, 1876, gives eleven genera and forty species, the eastern examples of which belong to India, Siam, Java, Borneo, Tartary, Thibet, Japan, and Formosa. Still more recently some belonging to the Western States of America have, I believe, been added by Cope or Coues, the latter informing us that up to the date of his paper, 1878, eighteen species and upwards of the rattlesnake proper had been described in the United States, nearly all in the west and south-west. So, as those vast deserts are being explored, new species are continually discovered.
Of the Indian species of Crotalidæ, those minus a rattle, Fayrer says that they are chiefly in Malaya and Indo-China. Many of them, the Trimeresuri, are arboreal, and like the foliage in colour. They have the viperine aspect, but are ‘less formidable than their American congeners,’ being of much smaller dimensions. Only one, Halys, has anything approaching to a rudimentary rattle, a tail ending in a spine. Of the Trimeresuri, the tree species, Fayrer affirms that few deaths are ascribed to them. Some attain to above three feet in length. He thinks a feeble person might die of their bite. They are of a sluggish habit, and lie quietly hidden among the leaves of low bushes and ferns. They will even suffer themselves to be moved without attempting to bite, but one that was pressed to the ground with a stick struck so hard as to break both its fangs. They feed chiefly on insects. Their habits are crepuscular if not nocturnal, and Fayrer does not state positively that they or any of the Indian Crotalidæ are viviparous.
Of the principal American Crotalidæ that are not true rattlesnakes, the ‘Bushmaster’ (Lachesis mutus) stands first. This is undoubtedly the largest venomous serpent known. In length it equals the Hamadryad; and in thickness, the large African vipers. On looking closely at the illustration of this reptile’s tail (p. 176), it will be seen that in addition to the spine which terminates it, there are several rows of fine, elaborated scales, which under the microscope appear almost as curiously pointed as those on the head of Vipera nasicornis. Dumeril thus describes the tail: ‘Ponctuée, et précédée de dix ou douze rangées d’écailles épineuses, un peu courbées en crochets à la pointe.’ This is the snake called Crotalus muet, or ‘dumb rattlesnake,’ by Linnæus, and which is supposed to simulate the sound of the rattle by vibrating this point against the leaves; but many other snakes do this whether their tail is pointed or not, as we saw in chap. xi. Any small thing, such as a twig rustling among dead leaves, would produce the same sound. The near approach of Lachesis to Crotalus horridus of the same habitat is, however, seen in this rudimentary rattle, the agitation of which may similarly be attributed to the timidity of these ‘highly nervous and irritable creatures,’ to repeat Coues’ words; for deadly as they are, timidity strongly displays itself. Watching the venomous snakes when their food is dropped into their cages, their excessive caution, amounting to cowardice, is remarkable, and this with the rattlesnakes especially. One will fix its eyes on the rat which is running about, and shrink back terrified if it approach too closely. Then if the quadruped is a moment quiet, the snake appears to be considering whether it will be advisable to attack it or not. Stealthily and slowly it approaches its head, but on the slightest movement of the little animal, recedes in alarm, and is some time before it makes a second venture. I have seen a rattlesnake thus timidly advancing and recoiling three or four times before it has the courage to give the fatal stroke. Even after the bite it watches its victim with a steadiness in which terror is the strongest expression; and when the rat has remained motionless for a time, and the rattlesnake ventures near to investigate and make sure it is dead, one faint gasp or dying struggle will cause the reptile to dart back in excessive alarm, and wait again some minutes before venturing near. After long and patient observations, I am still doubtful whether stupidity or timidity predominates in viperine natures.
Of the other well-known and formidable American Crotalidæ is the ‘Fer de lance’ (Trigonocephalus lanceolatus) of the Antilles and Central America. This has also a pointed tail. The Jararaca of Gray (Craspedocephalus Braziliensis) is another, but without the point. Of the true rattlesnakes, Dumeril gave five genera in 1844, viz. Crotalophorus, Crotalus, Caudisona, Urocrotalon, and Urosophus.
From the two species originally known, we see how they have gradually multiplied as the country has been more thoroughly explored. In 1860, Dr. Weir Mitchel affirmed that twenty species had been then described; probably the most recent ‘Reports’ or Bulletins will tell us of yet others. And these latter are exclusive of the non-rattle-bearing Crotalidæ.
Dr. Mitchel’s experiments were with the northern species, chiefly Cro. durissus; and as a relief from this wearisome classification, some of his observations will be welcome. One very noteworthy result is that the Crotalus does occasionally produce a sound independently of the rattle. Not a prolonged hiss, or by any means so loud as the innocent snakes, but merely ‘the expiration of air from the lungs just before striking.’ I have never observed or heard this in our London rattlesnakes, but it no doubt is of the same character and degree of sound as that produced by the Cerastes and the little Echis, and which more resembled a short, feeble, spitting sound. Still, as we are informed by Dumeril that rattlesnakes are ‘deprived of voice,’ it is interesting to know that, on the authority of Dr. Weir Mitchel, some slight sound, though not a regular hiss, does sometimes accompany the action of striking.
An inquiry has lately met the eye in one of our scientific journals as to whether a rattlesnake drinks. Dr. Mitchel clears away all doubts on that subject by impressing upon those who keep these creatures the importance of giving them plenty of water, particularly when changing the skin. Deprived of it, the cuticle comes off unhealthily—desquamates, in fact, in bits. At the casting of the cuticle, or previous to the process, they will not only drink, he tells us, but lie for hours in the water. When they were disinclined to eat, and had fasted long enough to endanger their health, he fed them by force with milk and insects, and the way he managed was to get their mouths open and insert a tunnel a safe distance down their throat. While held in this position, a repast consisting of insects and milk was pushed down the tube of the tunnel in sufficient quantities. The most surprising circumstance in connection with this style of feeding, and also with the process adopted by Dr. Shortt of Madras in filling his cobras ‘as full as they could hold’ with sour milk, is that these fastidious and frightened reptiles did not disgorge the diet. Both experimentalists, however, found it answer, reminding us of some advice given to the keeper at the London Ophidarium in the case of the Hamadryad, which, having no snakes to dine off one winter, elected to fast. To force frogs or fish down its throat was suggested; but no one could be found brave enough to undertake the task, and happily ‘Ophio’ survived till a relay of ring snakes arrived.
Both Mitchel and Coues corroborate what has been observed by others regarding the increased virulence of the bite when moulting; but both are of opinion that this is owing to an accumulation of venom, as the snakes have not been feeding or expending their store for some days. Even while not feeding, their venom is secreted all the same, and they survive many months, even a whole year and more, without food. Dumeril mentions one that lived twenty-five months without feeding.