HIBERNATION.

THE periodical torpor known as the winter sleep of reptiles is intimately connected with respiration, and a chapter must now be devoted to this subject.

‘Reptiles are obedient to the external atmosphere,’ has been aptly said of them. Thus, they obey the sun; for if exposed to his rays, they warm into life and activity. They obey the frost; for when exposed to its influence, their functions grow feeble or fail altogether, and they succumb to within a verge of lifelessness. They obey all the intermediate variations of temperature during the changing year, by displaying degrees of animation and activity responsive to the degree of warmth externally which they do not possess in themselves.

Bell speaks of hibernation as ‘amongst the most remarkable and interesting phenomena which occur in the history of animals.’ It is not a state of suffering, like that of a warm-blooded creature that is frozen to death; but with one common impulse, reptiles all retire, and remain in an almost lifeless repose, with every function so nearly suspended, that no external signs of existence are visible. For them it is a sort of rest, and we may cease to wonder at their longevity since they live only half their lives. It is, indeed, a convenient mode of getting through life, reminding us of a theory or proposal ventilated not long since, by which convicts were to be economically provided for by submitting them to a certain freezing process, and disposing them neatly on rows of shelves until the expiration of their term of punishment; all to be done then was to dust them thoroughly—perhaps scrub them a little—and restore them to the world and life again. And they were promised to be none the worse, not even to have lost their memory or to have acquired the rheumatism. Unfortunately the wonderful process has never been made clear to anxious inquirers, or some others of us, who are not convicts, might gladly resort to this method of rest occasionally, and of freezing out the worries of existence.

On the principle of political economy, this would be all very well, and in the great routine of nature there is beneficence in the hibernation of creatures, whether reptiles or other animals, that are sent to sleep at the very time when food fails them. The smaller members of the class have no longer insects and molluscs; the larger ones feed chiefly on rodents and birds which have also retired or migrated, or on their lesser kinsfolk, that no longer abound where most wanted by them. Therefore, this going to sleep every winter, and doing without food when there is no food to be had, is most convenient for a considerable section of animated nature.

There is something strangely analogous in the almost total suspension of vital forces in reptiles to that which vegetation undergoes. Circulation stops, the juices become stagnant, whether in a tree or in a snake, and it is sometimes difficult to decide in either case whether life is extinct or not. But with returning warmth comes renewed vitality; the fluids, whether of the animal or the vegetable organism, are thawed by the revivifying solar rays, which set them circulating and start the pulsation; and the animal machinery, like a watch wound up, is set in working order again.

It is owing to this lack of warmth in themselves that snakes can live only in hot countries, or in cooler latitudes, during the warmer weather, and not at all in the frigid zones. In speaking of them, Dumeril says LinnÆus was right in calling them cold animals in hot countries. ‘Aussi la plupart des Ophidiens habitent-ils les climats chauds, et c’est en parlant d’eux que LinnÉ a pu dire avec raison: “Frigida Æstuantium animalia.”’[47]

Dumeril describes their respiration as arbitrary, suspended, retarded, or accelerated at will. ‘La respiration Étant volontairement accÉlerÉe ou retardÉe, les actions chimiques et vitales qui en resultent doivent Être naturellement excitÉes ou ralenties par cette cause.’[48] ‘The electric fluid,’ says Latreille, ‘is one of the great agents in animating living beings; and upon reptiles it operates in conjunction with warmth in rousing them from their inactivity.’

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.

A few years ago, near Hayward’s Heath in Sussex, some men who were levelling the ground for building, dug out of a bank at a depth of from four to five feet, upwards of one hundred slow worms and as many small lizards, all in a torpid state. It was during February.

At the end of September more recently, a farmer in Wales, who with his labourers was removing a heap of manure, came upon an extraordinary bed of snakes and slow worms, and no less than 352 were killed, together with an enormous quantity of eggs; ‘thousands in clusters were destroyed.’ Three of the snakes were of immense size, and one hundred of them nine to twelve inches long.’ These latter were probably slow worms, and the three ‘immense’ ones ring snakes. One feels curious to know whether judgment for this act of wanton cruelty visited that farmer in a destruction of his crops next year by the mice and insects from which these harmless reptiles would have saved them!

The general reptilian instincts are the same in all climates where the temperature is similar. In Australia, as Krefft tells us, this is a grand time among schoolboys for ‘snake-hunting.’ They lay traps of large flat stones on open sunny ridges where the reptiles are likely to resort. Six to ten specimens of different species are often taken under one such stone. Even the venomous kinds may be easily captured and transferred to a bag in their half-dormant condition. Sometimes in lifting a stone, a dozen or more handsome and beautiful lizards are found among their ophidian cousins. The Wallaby hunters generally provide themselves with a collecting-bag, and thousands of snakes have thus been transferred to museums. So expert do the hunters become, that in eight years, the same author affirms, not one accident has occurred from a venomous species. From May to September in Australia, timid persons need be in no fear of snakes in the ‘scrub.’ The larger and more dangerous species retire deep into the ground, and only the young ones under stones. Warm days entice them out for an hour or two, and they retire again at night, just as is the case with those of the United States.

The ancients were aware of this hibernation of reptiles; and Pliny, who, having sometimes a foundation of fact to build upon, is all the more dangerous from his fabulous superstructure, writes, ‘The viper is the only serpent that conceals itself in the earth. It can live there without taking food for a whole year. They are not venomous when they are asleep,’ he sagely adds. Vipers can live without food for even more than a year, and so can other snakes; but this often is irrespective of hibernation, and of this more will be said presently.

A still stronger evidence of vitality or suspended animation is witnessed in the extraordinary custom of packing the poor wretched snakes in air-tight bottles, which some barbarous (the word here in both senses may be used) people adopt. A Cerastes arrived in England in a bottle, which had been hermetically closed for six weeks, and it revived. It was so crowded into the bottle as to look quite dead, but revived directly it was released, and struck a fowl, which died instantly! Sometimes a bottle or jar is literally crowded with ophidian captives, that are certainly out of harm’s way so far as others are concerned, and travel in a compact compass; but it stands to reason that even when they survive this close imprisonment, they are not in a very lively condition, and the large mortality which is found in most collections may be imputed to a great extent to the unhealthy condition in which they arrive after injudicious packing. Nailed up in air-tight boxes, is a very ordinary mode of transportation, a species of cruelty which would raise a cry of horror were the captive any other than a despised ‘reptile!’ In connection with breathing or not breathing, and powers of endurance, such packing receives only a passing mention here, but is one that should be thoroughly exposed in the Animal World and similar papers.

One more singular example of periodical repose, but which can scarcely be called either hibernation or estivation, is seen in the sea snakes, the HydrophidÆ of the Eastern Ocean. Of these Dr. Cantor affirms that they are seen so soundly asleep on the surface of the water, that a ship passing among them does not awaken them. This is the more remarkable because the eyes of sea snakes are organized to endure the glare of light only when modified or subdued through water, and are easily affected when out of it, the reptiles becoming dazzled, and even blinded, by bright sunshine. So that we must suppose some peculiar insensibility of nerve in these, or a cessation of active functions during their repose analogous to the hibernation of land snakes. Another interesting inquiry suggests itself: viz. How does one ascertain that an open-eyed snake is ‘asleep’? We called that Racer (p. 64) ‘asleep,’ as it appeared to be quite unconscious of interruption, and did not move at our approach.