The periodical torpor and insensibility which reptiles undergo cannot, however, be always associated with extremes of cold, nor in all cases called strictly a ‘winter’ sleep; because it is during the hottest seasons in the tropics that they resign themselves similarly to an almost death-like repose and temporary tomb, burying themselves in the mud, which is hard-baked around and over them, almost hermetically sealed until the rainy season loosens the soil, and frees them from this literal sarcophagus. In this case the so-called ‘hibernation’ is the result of drought. It is moisture now which revivifies them, rain which restores their vital functions, and like the chrysalis bursting its shell and emerging a new and brilliant creature, the reptile lives anew, doffs his muddy coat, and reappears in all his resplendent colouring.
The prairie rattlesnake (Crotalus confluentus) is known to undergo this species of torpor, which is, in fact, estivation. It is described as having been found in this ‘stupid condition’ in the dry cañons of the Rocky Mountains during the droughts of July and August. American naturalists who accompany the Exploring Expeditions affirm that this partial torpor is common to many species of snakes, and analogous to hibernation. They are ‘sluggish, stupid, blind, striking wildly,’ says one of the official Reports.
Snakes remain torpid on an average half the year. It is a winter sleep in colder and temperate climates, and a summer sleep in hot ones. The green garter-snake of the United States hibernates eight months out of the twelve. So do some of the Australian snakes, others being underground five months in the year, Krefft tells us. The duration of insensibility varies, of course, with the climate and season.
Snakes in menageries have been known to manifest inactivity and disinclination for food as early as September if the season be unusually cold, at other times in October; but, on the contrary, during a milder season they keep active until November, while some do not hibernate at all. Their habits there can, however, scarcely be cited as normal, since the artificial heat regularly maintained in the Ophidarium never permits the rigours of an out-door winter to affect them. Nevertheless they manifest the disposition for repose; and if it could be so arranged that the tropical snakes could be submitted to tropical heat and drought, and those of cooler countries to frosty air, as in a state of nature, we might witness both estivation and hibernation under the same roof.
A partial hibernation is observable in reptiles in captivity when, though not absolutely inactive, they decline food. For twenty-two weeks a python at the Zoological Gardens fasted during one winter; at another time, twenty weeks. The large python (reticulatus) fasted for one year and eleven months, covering two winters, but fed well and retained its health after this. Meanwhile, during this prolonged fast, should a gleam of sunshine penetrate the foggy atmosphere of our London winters, and shine through the glass roof upon a constrictor’s coverlet, he may slowly emerge therefrom, displaying a few feet of his lazy length for an hour or so, thus verifying the words, ‘obedient to the external atmosphere.’ No creatures are so susceptible of the changes of temperature; and the same degree which caused them to seek a retreat will, on the return of spring, reanimate them. And warmth—in them almost another word for vitality—equally affects their appetite. In the very height of summer, should their feeding-day prove a chilly one, a much lighter drain on the larder is observable, while a warm, bright day will show a heavy poulterer’s bill in re Ophidarium. Dr. A. Stradling, a practical ophiologist, found that the common English snakes ‘thrive exceedingly by reason of their increased appetites,’ when taken to the tropics. ‘It is impossible to say what degree of heat a reptile will not stand and enjoy,’ says this writer (Field, July 28, 1881). ‘On the hottest days in the hottest places on earth, one surprises snakes and lizards basking in the blazing sun-glare, on sands and rocks which it would almost blister the hand to touch.’ Florida is the most southern extreme of my own experience; but during a summer there one could not rest the hand on the almost burning stones and walls on which the reptiles delightedly reposed; and even in England, during a hot August, my little Bournemouth lizards were positively hot to the touch when basking in the full power of a bright noon sun. Dumeril corroborates these facts when he says some reptiles can endure a temperature higher than blood-heat. Sometimes in early spring he found a snake seeming to be asleep under a very hot wall which had been exposed to the mid-day sun, but which had been several hours in shadow. So tenaciously had the reptile retained the heat it had then absorbed, that though the air now felt cold, the snake imparted une chaleur très notable when he touched it. Many times, in taking up a lizard from a sunny rock in summer, it really has brulé les doigts.[49] The old fable about salamanders living in fire no doubt originates in the fact of reptiles loving heat as they do. Many pages might be filled with instances of this, and of their approaching fire to a suicidal extent.
Equally strange is the degree of cold to which they can sometimes submit, and yet recover. But we must conclude that this is when they are overcome gradually, not suddenly, by it, and not exposed to the outer air so that the tissues would be injured. Dr. Carpenter mentions reptiles having been kept three years in an ice-house, and recovering on being gradually restored to warmth. Too recklessly acting upon this, I deposited my pet lizards in a small, shallow box containing moss, sand, and soft rubbish, and left them outside a window to hibernate. They buried themselves as deeply as they could go,—only a few inches, alas!—but a sudden and severe frost set in, and the poor little victims were frozen stiff at the bottom of their prison-house. It was in a bleak north-eastern aspect, and the sharp frost easily striking through the wood, that slight box must have proved a very different sort of nest to what they would have chosen on their native heath,—far down, and well protected from the icy winds. In a strong, deep box, or an earthenware jar, with sufficient earth and rubbish in it, they might have survived.
In the Museum of Paris in 1875-76, sixteen rattlesnakes are said to have died of cold. The heating apparatus at the Jardin des Plantes is less effective than our own in London, where very few of the snakes have been known to suffer from lowered temperature.
Snakes are abundantly supplied with oily fat; thick layers of it line their intestines in autumn, and this is gradually absorbed during their torpor. They therefore lose weight, and awake in an enfeebled condition, only gradually recovering their normal strength after some days.
The power of endurance in serpents, and their independence of a large supply of oxygen, render them important agents in the economy of nature. In the swamps and morasses where malaria abounds, reptiles are most numerous. Many such places under canopies of pestilential vapours, swarm with insects, molluscs, worms, caterpillars, and the smaller reptiles on which snakes mostly feed. They are, therefore, the scavengers of such localities; they fulfil a great law by keeping up the balance of nature even to the extent of rendering certain countries habitable.
Those ophidian families which prefer higher lands, sandy or rocky districts, select the sunny hill-sides when the frost sets in, and hide themselves under stones or in caves where, as described in the chapter on rattlesnakes, they congregate in vast numbers. Piles and convolutions of serpents in this condition have often been discovered, and as often described. It is as if the small degree of animal warmth each one possessed were harvested for their mutual good, and to the benefit of the whole community. Nor are these assemblages at all exclusive as to kind, but are dens of discordant materials, where, as an American wrote, ‘the liberal terms of admission seemed only to require the evidence of snakeship.’ Lizards, too, though of widely-branching kinship, are guided by the same instinct, and sometimes share the retreat.