Snow Days

by Charlotte Overby
illustrations by Mark Raithel

Get ready to add a new cool word to your vocabulary.

You wake up before your alarm, flip on the radio and wait while the announcer finishes reading the headline news. Finally, he begins to run through school cancellations. You hold your breath as he rattles off a long list of schools you've never even heard of. At last he comes to yours and-yahoo!-no school. Snow day!

Outside, fresh snow covers everything, making the ground, cars, houses, trees and bushes look rounded and smooth. Some people stay cozy inside. Others bundle up first thing and explore the new landscape.

As the morning goes by, people shovel their sidewalks and steps. You may see tracks beneath the bushes left by squirrels or rabbits. Birds shake the delicate stacks of snow from power lines. Before long, signs of life are all over the snow.

But what about animals who move around and live under or in the snow? After all, there are still leaves, rotting logs, plants and rocks underneath it all. Snow doesn't make these habitats disappear. It changes them.

First, think about falling snow. As it begins to cover the ground, it doesn't fill every nook and cranny. Instead, grasses bend, logs and rocks form little caves and shelters, and the piled snow creates a system of tunnels and bridges. Ecologists call this place-above the ground but beneath the snow-the subnivean environment. You may be surprised to learn there are animals-even some insects-that move around and live in the snow.

In the northern United States and Canada, where snow remains on the ground for months at a time, several small mammals move about, sleep and find food beneath the snow until it melts in the spring. They may not venture above the snow for months. In northern snowy climates, these animals are true subniveans. Voles, shrews and some mice are examples.

If you could lift snow off the ground, you might see vole trails like these.

Even though Missouri doesn't stay buried in snow for months at a time, these animals become subniveans, even if only for short periods of time. Voles, for example, live in thickets, meadows or prairie grasslands. They build sturdy runways or paths both on top of and just below the ground. Nests are found in clumps of grass at the end of a path or below ground at the end of a short tunnel.

Voles have big appetites. In 24 hours they can eat their own weight in food. They move through their system of paths and tunnels eating roots, grasses and stalks of plants.

Just because it snows doesn't mean voles stop looking for food or moving around. After a snowfall, voles keep using their network of paths and trails. They tunnel through the snow, making use of natural bridges formed by bending grasses, piles of leaves and clumps of dirt. The snow helps keep them hidden from predators, such as owls and hawks, provided they don't venture out on top of the snow. Mice and shrews maneuver through the snow in a similar way and sometimes sleep in large groups to benefit from one another's body heat.

A good snowfall insulates subniveans and their habitat by keeping heat from radiating out of the earth. In some climates, 7 to 10 inches of snow on the ground actually will keep the soil surface a fairly constant 32 degrees-warmer than the above-ground air and warm enough for the subniveans to stay active. They are more vulnerable during winter months when the ground is bare and the temperatures drop below freezing. They must survive without a "blanket" of snow.

You can imagine furry mammals tunneling and networking through the snow, but what about insects? It's highly unlikely you'll be swatting mosquitoes or watching for ticks this winter, but how about fleas? Snow fleas?

Snow fleas are the most common members of a group of insects called springtails. They are small-only a few millimeters-and people only notice them when they cluster together in large groups on top of snow or wet leaves, often near tree trunks or exposed logs. They look a bit like pepper sprinkles on the snow, only the pepper is constantly moving.

In spite of their name they are not related to fleas that bother pets and wildlife, but they "jump" like fleas. Their abdomens are equipped with two prongs that bend around and underneath the insect. The prongs are held in place, or cocked, by two hooks located on the insect's body. When the hooks open, the prongs spring against the ground, and the insect leaps through the air.

Springtails emerge from the ground during the day to absorb heat from the sun, feeding on algae, bacteria and fungi on the surface of the snow. Watch for them on melting spots of snow in the woods. Sometimes you can spot them near icicles. When they jump, they seem to disappear completely. Snow fleas do no harm and are part of the complex of organisms that break down leaf and other organic matter on the forest floor.

Next time you have a snow day, wander around outside and watch for signs of life in the snow. Build a fort or tunnel through a plow bank of snow and become a subnivean yourself-for an afternoon at least. Imagine what real snow days are like for animals and insects.