_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.
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