Popular Science Monthly/Volume 50/February 1897/How Plants and Animals Spend the Winter
|HOW PLANTS AND ANIMALS SPEND THE WINTER.|
STATE GEOLOGIST OF INDIANA.
ONE of the greatest problems which each of the living forms about us has had to solve during the years of its existence on earth is how best to perpetuate its kind during that cold season which once each year, in our temperate zone, is bound to come. Many are the solutions to this problem. Each form of life has, as it were, solved it best to suit its own peculiar case, and to the earnest student of Nature there is nothing more interesting than to pry into these solutions and note how varied, strange, and wonderful they are.
To fully appreciate some of the facts mentioned below it must be borne in mind that there is no such thing as "spontaneous generation" of life. Every cell is the offspring of a pre-existing cell. Nothing but a living thing can produce a living thing. Hence every weed that next season will spring up and provoke the farmer's ire, and every insect which will then make life almost intolerable for man or beast, exists throughout the winter in some form.
If we begin with some of the lowly plants, such as the freshwater algæ, or so-called "frog-spittle" of the ponds, and many of the rusts and fungi which are so injurious to crops, we find that they form in autumn "resting spores." These are very small and globular, one-celled bodies, having a much thicker coat and denser protoplasm or contents than are found in the spores often produced in summer by the same plants, and which are destined for immediate growth. The power of life within these winter resting spores is proof against the severest attacks of frost, and they lie snugly ensconced in the mud at the bottom of pond or stream, or buried beneath the leaves in some sheltered nook, until the south winds of March or April furnish the key to unlock the castle of the ice king. Then the spirit of growth within each spore begins to assert itself once more, and, bursting the walls, the contents soon produce the parent or summer form of the plant with which we are most familiar. Thus the spores which next season will produce the grape mildew and the red rust of wheat are now in existence, the former within the substance of the fallen grape leaf, the latter within the stubble or about the roots of last season's wheat plants.
If the grape leaves should be carefully gathered and burned, and the stubble destroyed in like manner, not only would the next season's crop of these two parasitic plant pests be wonderfully lessened, but many injurious insects would at the same time be destroyed.
Higher in the scale of plant life we find the flowering annuals bending all their energies during the summer to produce that peculiar form, the "seed," which is only a little plant boxed up to successfully withstand the rigors of winter. The great sunflower, that grows into a giant in a single season and defies the summer sun and storm, falls an easy victim to the frosts of autumn. It, however, prepares the way for many successors in the ripened seeds, each one of which, under favorable conditions, will germinate, grow, reproduce its kind, and thus complete another cycle in the realm of vegetable life. The prospective life and activity of a whole field of next summer's waving corn may be considered as stored up in a few pecks of comparatively lifeless seed corn safely housed in the granary. Within its two protective coats and surrounded by a large store of food, in the form of seed leaf or nucleus, to be used when growth begins again, each little plantlet lives and survives the coldest blasts of King Boreas and his cohorts.
Note, too, the buds and underground stems which will furnish the beginning of next season's growth of our biennial and perennial plants. See how they are protected by heavy overcoats in the form of bud scales. Oftentimes, too, as in the hickory and "balm of Gilead" trees, these scales have a coat of resin or gum on the outside to render them waterproof; and some, as those of the pawpaw, are even fur-lined, or rather fur-covered, with a coating of soft black hairs. Were these protective scales not present, the tender shoots within them, which will furnish the nucleus of next season's foliage, would be seared and withered by the first frost as quickly as though touched with a red-hot iron.
The above are some of the many ways in which our plants, in the course of ages and many changes of environment, have solved the problem of surviving the cold of winter. Moreover, they always prepare for this cold in time, the resting spores and seeds being ripened and the bud scales formed over the tender tips of the branches long before the first severe frost appears.
Let us now glance at those higher forms of life called animals—"higher," because they are absolutely dependent upon plants for their food—and see how they pass away their time while their food-producers, the plants, are resting.
Beginning with the earthworms and their kindred, we find that at the approach of winter they burrow deep down where the icy breath of the frost never reaches, and there they live during the cold season a life of comparative quiet. That they are exceedingly sensitive to warmth, however, may be proved by the fact that when a warm rain comes some night in February or March, thawing out the crust of the earth, the next morning reveals the mouths of hundreds of the pits or burrows of these primitive tillers of the soil in our dooryard, each surrounded by a little pile of pellets, the castings of the active artisans of the pit during the night before.
If we will get up before dawn on such a morning we can find the worms crawling actively about over the surface of the ground, but when the first signs of day appear they seek once more their protective burrows, and only an occasional belated individual serves as a breakfast for the early birds.
The eyes of these lowly creatures are not visible, and consist of single special cells scattered among the epidermal cells of the skin, and connected by means of a sensory nerve fiber with a little bunch of nervous matter in the body. Such a simple visual apparatus serves them only in distinguishing light from darkness, but this to them is most important knowledge, as it enables them to avoid the surface of the earth by day, when their worst enemies, the birds, are in active search for them.
The fresh-water mussels and snails and the crayfish burrow deep into the mud and silt at the bottom of ponds and streams where they lie motionless during the winter. The land snails, in late autumn, crawl beneath logs, and, burrowing deep into the soft mold, they withdraw far into their shells. Then each one forms with a mucous secretion two thin, transparent membranes, one across the opening of the shell and one a little farther within, thus making the interior of the shell perfectly air-tight. There for five or six months he sleeps free from the pangs of hunger and the blasts of winter, and when the balmy breezes of spring blow up from the south he breaks down and devours the protecting membranes and goes forth with his home on his back to seek fresh leaves for food and to find for himself a mate.
Next in the scale come the insects, which comprise four fifths of all existing animals, and each one of the mighty horde seen in summer has passed the winter in some form. One must look for them in strange places and under many disguises, for they can not migrate, as do the majority of the birds, nor can they live an active life while the source of their food supply, the plants, are inactive.
The majority of those insects which next May or June will be found feeding on the buds or leaves of our trees, or crawling wormlike over the grass of our lawns, or burrowing beneath the roots of our garden plants, are represented in the winter by the eggs alone. These eggs are deposited in autumn by the mother insect, on or near the object destined to furnish the young, or larvae, their food. Each egg corresponds to a seed of one of our annual plants, being, like it, but a form of life so fashioned and fitted as to withstand for a long period intense cold; the mother insect, like the summer form of the plant, succumbing to the first-severe frost.
Thus myriads of the eggs of grasshoppers are in the early autumn deposited in the ground, in compact masses of forty to sixty each. About mid-April they begin to hatch, and the sprightly little insects, devoid of wings, but otherwise like their parents, are seen on every hand.
A comparatively small number of insects pass the winter in the larval or active stage of the young. Of these, perhaps the best known is the brown "woolly worm" or "hedgehog caterpillar," as it is familiarly called. It is thickly covered with stiff black hairs on each end, and with reddish hairs on the middle of the body. These hairs appear. to be evenly and closely shorn, so as to give the animal a velvety look; and as they have a certain degree of elasticity, and the caterpillar curls up at the slightest touch, it generally manages to slip away when taken into the hand. Beneath loose bark, boards, rails, and stones, this caterpillar may be found in midwinter, coiled up and apparently life-less. On the first bright, sunny days of spring it may be seen crawling rapidly over the ground, seeking the earliest vegetation which will furnish it a literal "breakfast." In April or May the chrysalis, surrounded by a loose cocoon formed of the hairs of the body interwoven with coarse silk, may be found in situations similar to those in which the larva passed the winter. From this, the perfect insect, the Isabella tiger moth, emerges about the last of June. It is a medium-sized moth, dull orange in color, with three rows of small black spots on the body, and some scattered spots of the same color on the wings.
By breaking open rotten logs one can find in midwinter the grubs or larvæ of many of the wood-boring beetles, and, beneath logs and stones near the margins of ponds and brooks, hordes of the maggots or larvæ of certain kinds of flies may often be found huddled together in great masses. The larvæ of a few butterflies also live over winter beneath chips or bunches of leaves near the roots of their food plant, or in webs of their own construction, which are woven on the stems close to the buds whose expanding leaves will furnish them their first meal in spring.
Many insects pass the winter in the quiescent or pupal stage; a state exceedingly well fitted for hibernating, requiring, as it does, no food, and giving plenty of time for the marvelous changes which are then undergone. Some of these pupæ are inclosed in dense silken cocoons, which are bound to the twigs of the plants upon which the larvae feed, and thus they swing securely in their silken hammock through all the storms of winter. Perhaps the most common of these is that of the brown Cecropian moth, the large oval cocoon of which is a conspicuous object in winter on the twigs of our common shade and fruit trees. Many other pupæ may be found beneath logs or on the under side of bark, and usually have the chrysalis surrounded by a thin covering of hairs, which are rather loosely arranged. A number pass the cold season in the earth with no protective covering whatever. Among these is a large brown chrysalis with a long tongue-case bent over so as to resemble the handle of a jug. Every farm boy has plowed or spaded it up in the spring, and it is but the pupa of a large moth, the larva of which is the great green worm with a "horn on its tail," so common on tomato plants in the late summer.
Each of the winter forms of insects above mentioned can withstand long and severe cold weather—in fact, may be frozen solid for weeks and retain life and vigor, both of which are shown when warm weather and food appear again. Indeed, it is not an unusually cold winter, but one of successive thawings and freezings, which is most destructive to insect life. A mild winter encourages the growth of mold which attacks the hibernating larvæ and pupæ as soon as, from excess of rain or humidity, they become sickly; and it also permits the continued activity of insectivorous mammals and birds. Thus, moles, shrews, and field mice, instead of burying themselves deeply in the ground, run about freely during an open winter, and destroy enormous numbers of pupæ; while such birds as the woodpeckers, titmice, and chickadees are constantly on the alert, and searching in every crevice and cranny of fence and bark of tree for the hibernating larvæ.
Of the creeping, wingless creatures which can ever be found beneath rocks, rails, chunks, and especially beneath those old decaying logs which are half buried in the rich vegetable mold, the myriapods, or "thousand-legs," deserve more than passing notice. They are typical examples of that great branch of the animal kingdom known as arthropods, which comprises all insects and crustaceans. Each arthropod has the body composed of rings placed end to end and bearing jointed appendages, and in the myriapods each ring and its appendages can be plainly seen, whereas in the higher forms of the branch many of the rings are so combined as to be very difficult to make out.
Full forty kinds of myriapods occur in any area comprising one hundred square miles in the eastern United States. About twenty-five of them go by the general name of "thousand-legs," as each has from forty to fifty-five cylindrical rings in the body, and two pairs of legs to each ring. The other fifteen belong to the "centiped" group, the body consisting of about sixteen flattened segments, or rings, each bearing a single pair of legs. When disturbed, the "thousand-legs" always coils up and remains motionless, shamming death, or "playing ’possum," as it is popularly put, as a means of defense; while the centiped scampers hurriedly away and endeavors to hide beneath leaf, chip, or other protecting object. All those found in the Northern States are perfectly harmless, the true centiped, whose bite is reputed much more venomous than it really is, only being found in the South. True, some of the centiped group can pinch rather sharply with their beetle-like jaws, and one, our largest and most common species, a brownish-red fellow about three inches long and without eyes, can even draw blood if its jaws happen to strike a tender place. When handled, it always tries to bite, perhaps out of revenge for the abominably long Latin name given it by its describer. In fact, the name is longer than the animal itself—Sco-lo-po-cryp-tops sex-spi-no-sa being its cognomen in full. With such a handle attached to it, who can blame it for attempting to bite? Yet to the scientist up on his Latin each part of the above name bears a definite and tangible meaning. All the myriapods found in the woods and fields feed upon decaying vegetation, such as leaves, stems of weeds, and rotten wood, and in winter three or four species can usually be found within or beneath every decaying log or stump. One species with very long legs is often found in damp houses or in cellars. It is sometimes called the "wall-sweeper," on account of its rapid, ungainly gait, and is even reputed to prey upon cockroaches and other household pests.
Spiders, which do not undergo such changes as do most of the common, six-footed insects, winter either as eggs or in the mature form. The members of the "sedentary" or web-spinning group, as a rule, form nests in late autumn, in each of which are deposited from fifty to eighty eggs, which survive the winter and hatch in the spring, as soon as the food supply of gnats, flies, and mosquitoes appears. The different forms of spiders' nests are very interesting objects of study. Some are those close-spun, flat, button-shaped objects, about half an inch in diameter, which are so common in winter on the under side of bark, chunks, and flat rocks. Others are balloon-shaped and attached to weeds. "Within the latter the young spiders often hatch in early winter, make their first meal off their empty egg cases, and then live together in hunger and harmony until the south winds blow again, when they emerge and scatter far and wide in search of sustenance.
The "wandering" spiders never spin webs, but run actively about and pounce upon their prey with a tiger-like spring. Six or eight of the larger species of this group winter in the mature form beneath logs and chunks, being often frozen solid during cold weather, but thawing out as healthy as ever when the temperature rises. Retiring beneath the loose-fitting bark of hickory or maple trees, a number of the smaller tube-weaving spiders construct about themselves a protecting web of many layers of the finest silk. Within this snug retreat they lie from November until April—a handsome, small, black fellow, with green jaws and two orange spots on his abdomen, being the most common species found motionless within this seeming shroud of silk on a day in midwinter.
In any Northern State as many as four hundred different kinds of the six-footed or true insects, in the winged or adult stage, may be taken in winter by any one who is so disposed, and knows where to search for them. Among the Orthoptera there are a half dozen or more grasshoppers which, when full grown, are less than half an inch in length, gray or blackish in color, and with the hard upper crust of the thorax extending the full length of the body and covering the wings. They are called "grouse grasshoppers," and daring cold weather they hide beneath the loose bark of logs, or beneath the bottom rails of the old Virginia worm fences. From these retreats every warm, sunny day tempts them forth in numbers. On such occasions the earth seems to swarm with them, as they leap before the intruder, their hard bodies striking the dead leaves with a sound similar to that produced by falling hail. The common field cricket belongs also to the Orthoptera, and the young of various sizes winter under rails and logs, bidding defiance to Jack Frost from within a little burrow or pit beneath the protecting shelter.
The true bugs, or Hemiptera, hibernate in similar places; squash bugs, chinch bugs, "stink" bugs, and others being easily found in numbers beneath loose bark or hidden between the root leaves of mullein and other plants.
Nearly three hundred species of Coleoptera, or beetles, occupy similar positions. Almost any rotten log or stump when broken open discloses a half dozen or more "horn" or "bess beetles"—great, shining, clumsy, black fellows with a curved horn on the head. They are often utilized as horses by country children, the horn furnishing an inviting projection to which may be fastened, by a thread or cord, chips and pieces of bark to be dragged about by the strong and never lagging beast of burden. When tired of "playing horse" they can make of the insect an instrument of music, for, when held by the body, it emits a creaking, hissing noise, produced by rubbing the abdomen up and down against the inside of the hard, horny wing covers. This beetle passes its entire life in cavities in the rotten wood on which it feeds, and when it wishes a larger or more commodious home it has only to eat the more.
The handsome and beneficial lady beetles winter beneath fallen leaves or between and beneath the root leaves of the mullein and the thistle. Our most common species, the thirteen-spotted lady beetle, is gregarious, collecting together by thousands on the approach of cold weather, and lying huddled up like sheep until a "breath of spring" gives them the signal to disperse. Snout beetles galore can be found beneath piles of weeds near streams and the borders of ponds or beneath chunks and logs in sandy places. All are injurious, and the farmer by burning their hibernating places in winter can cause their destruction in numbers. Rove beetles, ground beetles, and many others live deep down in the vegetable mold beneath old logs, where they are, no doubt, as secure from the breath of the ice king as if they had followed the swallow to the tropics.
Of the Diptera, or flies, but few forms winter in the perfect state, yet the myriads of house flies and their kin, which next summer will distract the busy housewife, are represented in winter by a few isolated individuals which creep forth occasionally from crevice or cranny and greet us with a friendly buzz.
In midwinter one may also often see in the air swarms of small, gnatlike insects. They belong to this order, and live beneath the bark of freshly fallen beech and other logs. On warm, sunny days they go forth in numbers for a sort of rhythmical courtship; their movements while in the air being peculiar in that they usually rise and fall in the same vertical line—flitting up and down in a dreamy, dancing sort of motion.
Among the dozen or more butterflies and moths which winter in the perfect state the most common and the most handsome is the "Camberwell Beauty" or "Mourning Cloak," a large butterfly whose wings are a rich purplish brown above, duller beneath, and broadly margined with a yellowish band. It is often found in winter beneath chunks which are raised a short distance above the ground or in the crevices of old snags and fence rails. It is then apparently lifeless, with the antennæ resting close along the back, above which the wings are folded. But one or two warm days are necessary to restore it to activity, and I have seen it on the wing as early as the 2d of March, hovering over the open flowers of the little snow trillium.
All the species of ants survive the winter as mature forms, either in their nests in the ground or in huddled groups in half-rotten logs and stumps, while here and there beneath logs a solitary queen bumblebee, bald hornet, or yellow jacket is found—the sole representatives of their races.
Thus insects survive the winter in many ways and in many places, some as eggs, others as larvæ, still others as pupæ, and a large number as adults—all being able to withstand severe cold and yet retain vitality sufficient to recover, live, grow, and replenish the earth with their progeny when the halcyon days of spring appear once more.
In the scale of animal life the vertebrates or backboned animals succeed the insects. Beginning with the fishes, we find that in late autumn they mostly seek some deep pool in pond or stream at the bottom of which the water does not freeze. Here the herbivorous forms eke out a precarious existence by feeding upon the innumerable diatoms and other small plants which are always to be found in water, while the carnivorous prey upon the herbivorous, and so maintain the struggle for existence. The moving to these deeper channels and pools in autumn and the scattering in the spring of the assembly which has gathered there constitute the so-called migration of fishes, which is far from being so extensive and methodical as that practiced by the migratory birds.
Many of the smaller species of fishes, upon leaving these winter resorts, ascend small, clear brooks in large numbers for the purpose of depositing their eggs, as, when hatched in such a place, the young will be comparatively free from the attacks of the larger carnivorous forms. Among the lowest vertebrates often found in numbers in early spring in these meadow rills and brooks is the lamprey, or "lamper eel," as it is sometimes called. It has a slender, eel-like body, of a uniform leaden or blackish color, and with seven purse-shaped gill openings on each side. The mouth is fitted for sucking rather than biting, and with it they attach themselves to the bodies of fishes and feed on their flesh, which they scrape off with their rasplike teeth. Later in the season they disappear from these smaller streams, probably returning in midsummer to deeper water. Thoreau, who studied their habits closely, says of them: "They are rarely, seen on their way down stream, and it is thought by fishermen that they never return, but waste away and die, clinging to rocks and stumps of trees for an indefinite period; a tragic feature to the scenery of the river bottoms worthy to be remembered with Shakespeare's description of the sea floor."
A few of the fishes, as the mud minnow and smaller catfishes, together with most frogs, turtles, and salamanders, on the approach of winter, burrow into the mud at the bottom of the streams and ponds, or beneath logs near their margins. There they live without moving about and with all the vital processes in a partially dormant condition, thus needing little if any food.
The box tortoise or "dry-land terrapin," the common toad, and some salamanders burrow into the dry earth, usually going deep enough to escape the frost, while snakes seek some crevice in the rocks or hole in the ground where they coil themselves together, oftentimes in vast numbers, and prepare for their winter's sleep. If the winter be an "open" one this hibernation is sometimes interrupted, and the animal issues forth from its retreat on a warm, sunny day, thinking, no doubt, that spring has come again.
Thus the writer has, on one occasion, seen a soft-shelled turtle moving gracefully over the bottom of a stream on a day in late December, and has in mid-January captured snakes and salamanders from beneath a pile of driftwood where they had taken temporary refuge.
With frogs especially this hibernation is not a perfect one, and there is a doubt if in a mild winter some species hibernate at all. For example, the little cricket frog or "peeper" has been seen many times in midwinter alongside the banks of flowing streams, and during the open winter of 1888–’89 numerous specimens of leopard and green frogs were seen on different occasions in December and January, while on February 18th they, together with the peepers, were in full chorus.
Of our mammals, a few of the rodents or gnawers, as the ground-hogs, gophers, and chipmunks, hibernate in burrows deep enough to escape the cold, and either feed on a stored supply of food, or, like the snakes and crayfish, do not feed at all.
Others, as the rabbits, field mice, and squirrels, are more or less active and forage freely on whatever they can find, eating many things which in summer they would spurn with scorn. To this class belongs that intelligent but injurious animal the musquash or muskrat. Those which inhabit the rivers and larger streams live in burrows dug deep beneath the banks, but those inhabiting sluggish streams and ponds usually construct a conical winter house about three feet in diameter and from two to three feet in height. These houses are made of coarse grasses, rushes, branches of shrubs, and small pieces of driftwood, closely cemented together with stiff, clayey mud. The top of the house usually projects two feet or more above the water, and when sun-dried is so strong as to easily sustain the weight of a man. The walls are generally about six inches in thickness and are very difficult to pull to pieces. Within is a single circular chamber with a shelf or floor of mud, sticks, leaves, and grass, ingeniously supported on coarse sticks stuck endwise into the mud after the manner of piles. In the center of this floor is an opening, from which six or eight diverging paths lead to the open water without, so that the little artisan has many avenues of escape in case of danger. These houses are often repaired and used for several winters in succession, but are vacated on the approach of spring. During the summer the muskrat is, in the main, a herbivorous animal, but in the winter necessity develops its carnivorous propensities and it feeds then mainly upon the mussels and crayfish which it can dig from the bottom of the pond or stream in which its house is built.
The bats pass the winter in caves, the attics of houses and barns, or in hollow trees, hanging downward by their hind claws, eating nothing and moving not. All the carnivora, or flesh-eaters, as the mink, skunk, opossum, fox, and wolf, are in winter active and voracious, needing much food to supply the necessary animal heat of the body. Hence they are then much more bold than in summer, and the hen yard or sheep pen of the farmer is too frequently called upon to supply this extra demand.
But of all our animals it seems to us the birds have solved the winter problem best. Possessing an enduring power of flight and a knowledge of a southern sunny sky, beneath which food is plentiful, they alone of the living forms about us have little fear of the coming of the frost. True, forty or more species remain in each of the Northern States during the cold season, but they are hardy birds which feed mainly on seeds, as the snow bird and song sparrow; on flesh, as the hawks and crows; or on burrowing insects, as the nuthatches and woodpeckers. And no winter day is too dull and dreary, no sky too leaden and cheerless, no north wind too harsh and biting for them to be on the lookout for food.
Such are some of the solutions to the problem of life in winter which the plants and animals about us have worked out; such some of the forms which they undergo, the places which they inhabit.
To the thinking mind a knowledge of these solutions but begets other and greater problems, such as how can a living thing be frozen solid for weeks and yet retain vitality enough to fully recover? How can a warm-blooded animal sleep for months without partaking of food or drink? And, greater than either. What is that which we call life?
I hold in my hand two objects, similar in size, color, organs, everything—twins from the same mother in all outward respects. One pulsates and throbs with that which we call "life." It possesses heat, bodily motion, animal power. The other is cold, motionless, pulseless, throbless—a thing of clay. What is that "life" which the one possesses and the other lacks? Ah, there's the rub! With the wisest of men we can only answer, "Quien sabe?" (Who knows?)