Snow Critters

by Bill Amos, Vermont, US


Winter brings stress, crisis, behavioral and metabolic languor to most wild creatures. Some, like summer birds and a few butterflies in search of warmer climes, avoid harsh conditions by leaving the north, while many resident animals hibernate in winter-long torpor. For others, life is over by the end of summer, their legacy left in protected eggs. Mammals, active or asleep, grow thick insulating coats, and spiders and insects descend from treetops to find shelter close to the ground. Earthworms, toads, salamanders, and reptiles seek refuge as far underground as possible where, with altered lifestyle, their body fluids become resistant to freezing.

Birds that remain in the north cram themselves at our feeders. Chipmunks, woodchucks, and bears sleep in their winter quarters, and deer hunker down in protected forest glades. Grasshoppers and field crickets vanish completely, leaving only their eggs in the soil, while mole crickets (and moles themselves) dig deep beneath the frost line. Although torpid wasps remain more or less isolated in nests or sheltered crannies, bees in their hives and ants in subterranean chambers huddle together where the slowed metabolism of their combined body mass is sufficient to generate a bit of warmth.

There is only one cardinal rule for animals in winter: survive.

Winter not only brings rigors, it brings solutions too. In the depth of winter, life is everywhere around us—on, in, and beneath snow. Life of many kinds remains plentiful under ice-covered ponds and streams. Snow and ice are superb insulators for plants and animals underneath. Small creatures may not be in evidence, but all we need do is look in the right places.

It is no surprise that moths and butterflies survive the winter under conditions other than as adults; they exist as eggs and in immature stages. What truly startles is the sudden fluttering of a small moth across the snow on a mild February day. You might even come across a conspicuous Mourning Cloak butterfly hibernating in an unheated shelter. I discovered one in my garage last winter.

The usual winter evidence of moths and butterflies is either a dormant caterpillar or a transformational pupa, bare or wrapped in a silken cocoon. Larvae and pupae of all sorts of insects are found in forest litter, in chambers deep in the earth, tucked into the inner recesses of an old stone wall, burrowed into last summer's plant stalks. If you seek insects in the rough bark of trees, search the sunny side of a trunk, not the colder north side. Examine knot-holes and woodpecker borings, as nuthatches do. Out in the fields, each swollen goldenrod gall contains a tiny moth or fly waiting to emerge in spring.

A decomposing log on the forest floor not only is soft enough to permit entry, but its bacterial decay creates warmth that comforts as it provides safe haven for insects, spiders, centipedes, millipedes, worms, and snails. Such creatures also find protection in forest soil, an earthen incubator warmer than soil in open meadows where the frost line plunges three or four feet deep in our north country. A covering blanket of forest leaf litter alone, with its labyrinth of insulating air spaces and frosty cover, provides winter shelter for a wide array of small active creatures.

A few insects are true denizens of winter. Snow fleas assemble at the base of a tree where warmth creates melt-water on a sunny day. Hordes of these tiny primitive springtails may blacken sunken patches of snow, such as footprints and tire tracks. How do they survive and what do they eat? Their active metabolism (also that of many winter and high-altitude insects) is due to a natural antifreeze. Micro-algae and decaying plant material constitute their staple food. One kind of snow flea eats smaller springtails, but when the sap rises late in winter, most species congregate near outbreaks of the sweet flow.

In early winter, I may discover scorpion fly larvae and pupae around the base of a tree trunk, or in leaf litter. Later on, fat-bodied, long-legged adult scorpion flies emerge and darken patches of snow. Wingless, with a long pointed head, a scorpion fly looks like no other fly we're familiar with.

Another flightless insect, the snow fly, is a crane fly whose summer relatives resemble giant mosquitoes. Not the winter species, however, which lacks wings and has long fuzzy legs. Most of the winter it remains in leaf litter or under logs and stones, but on mild, sunny days, snow flies crawl over the snow in search of mates. Resembling little spiders, it takes a sharp eye to determine what they really are.

If I visit our ice-rimmed brook and turn over stones in the swift frigid current, I'll surely find stonefly nymphs. It is even more amazing when large stonefly adults emerge into winter air to fly, feed, and mate as a natural part of their life cycle. It is said that some years they even swarm and alight in huge numbers upon snow-laden trees, although I've seen no more than a few individuals on my forays.

Immature insects of many sorts are present in an icy brook, with mayfly nymphs and water pennies (beetle larvae) as the most predictable. They and stonefly nymphs find plenty to eat by gathering dead insects and plant fragments that whirl downstream in the swift, swollen current. This is not a time of stress for them, because cold-adapted brook insects are present throughout the year. As we brook-dabblers know well, the summer temperature of a clear little upland stream still carries a touch of winter.

Low temperatures are a problem for terrestrial insects if excess moisture is present, so many species rid themselves of as much body water as they can before the onset of winter, converting what remains into a form that is incorporated into cell substance, thus resisting freezing and crystallization that destroys tissues.

In northern New England each kind of insect copes with winter differently. If disturbed in their winter quarters, some stir themselves at once, while others require hours of warmth before they can move. With the onset of autumn, many insects are frantic to complete a portion of their life cycle: mating, laying eggs, or eating their last meal as a larva before metamorphosing into a pupa. Some settle into the first available protected spot, while others seek exactly the right sort of place— a certain kind of plant stem to bore into, for example—before coming to rest. Numerous adult insects die after ovipositing, their kind surviving through winter only as tiny protected eggs.

While winter is the peak season for snow insects and presents few problems for brook creatures, the rest of the insect world remains quietly unseen. Inactivity leading to dormancy may begin as early as late summer in some species, but for others December's cold is required to put them into a torpid state. Name your insect and it is here—somewhere.

Much the same can be said for spiders. Some adults survive by preparing a winter nest of silken webbing under loose bark within which they are insulated from the cold. Other spiders die in autumn, but their kind lasts through the winter as undeveloped eggs. In several species, young spiderlings hatch out, then remain in a communal webbed egg sac through the winter. Those spiders that hibernate in leaf litter and in rock piles often are not deeply asleep, and on mild winter days may crawl about in search of insect food that is plentiful and easy to secure in its dormant state.

Young spiders often take refuge in moss, and should you bring a clump into the house, be prepared to have spiderlings and many other little hibernating creatures crawl out as warmth unlocks their muscles and increases their metabolism and consumption of oxygen. If you insist on poking about in moss—or leaf litter or under rocks—you will surely also come across hibernating land snails, deeply withdrawn into their shells and protected with a mucus plug or, if so-equipped, behind an operculum, a "door" expressly designed for protection at any time of year.

Last month, within an hour after bringing our just-cut Christmas tree in from the cold, little critters skittered across the living room floor. They were gathered in a jar and taken outdoors to a nearby treeline where I brushed away snow and scooped up a bit of leaf litter, dumped the jar's contents into the depression, then covered it with a thick layer of leaves. Christmas is a time to be particularly considerate of others, even the least of those amongst us, and it seemed to me that the gift of life was the least I could do for small creatures rudely awakened from their winter sleep.

1999 William H. Amos

Comments to the author Comments to the author sent via our contacts page quoting page url plus : ('wamos','')">Bill Amos welcomed.

Bill Amos, a frequent contributor to Micscape, is a retired biologist living in the wooded hill country of Vermont in northern New England. He is an active microscopist and author of many natural history books and articles.

Editor's note: Other articles by Bill Amos are in the Micscape library (link below). Use the Library search button with the author's surname as keyword to locate them.


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Published in January 1999 Micscape Magazine.

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