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Winter is upon us and a paddle down the river reveals little in the way of insect life. However, insects are present in the winter, and often in incredible numbers. But due to their very small size, they are often overlooked.
Springtails get their name from two small prongs at the end of their body. The prongs are folded under the body and held in place by two hooks on their belly. When the hooks are released, the prongs spring backwards, propelling the springtail into the air. This, along with their six tiny legs are their only means of locomotion. Since they lack wings, they are unable to fly.
Springtails are among the most common insects on earth. One farmer's field in Ohio counted over a million insects per square meter! But for all their large numbers, they are often hard to find because of their small size. Most species of springtails are less than a tenth of an inch long! And because of their small size and springing method of movement, they seem to appear and disappear before your very eyes.
Once, while walking through the woods in late fall, I heard a light rainfall on the dry fallen leaves. This puzzled me because, looking up at the sky, I noticed it was a beautiful sunny day. Kneeling down on the forest floor to investigate the sound, I noticed countless millions of springtails. It was their jumping on the dry leaves that made the rainfall sound.
Springtails feed on decaying plant and animal material. They also need a constant supply of moisture since their bodies are not waterproof and they would soon dehydrate in dry conditions. Therefore, they can most often be found under the forest leaf liter, where it is always moist. Some types of springtails embark on long (for them) migrations lasting a couple of days. Perhaps the springtails I heard that fall day were migrating. If they were, I wonder where they were going and for what purpose.
Snow Fleas are a type of springtail whose migrations are easily observed. They are active as adults during the winter. The best time to observe their migration is a warm day after a snowfall. During the day, they will emerge from under the snow around tree trunks where the snow has melted, and head off across the snow. To find them, look for snow that looks like it has been sprinkled with pepper. Watch the pepper grains. If they seem to appear and disappear as if by magic, you have found the snow fleas. Another good place to look is in your footprints in the snow. While good jumpers for their size, if they fall into a footprint, they can't jump out. As the herd of snow fleas move across the snow, more and more fall into the footprint, sometimes collecting in large numbers.
Some springtails are aquatic, spending their lives on the surface of the water of ponds or streams. Often they collect in large numbers. I have seen gatherings of these springtails as large as a meter square and half an inch thick. How many layers of springtails on top of each other this represents, I don't know. One of these colonies had collected on a small stream . Since the stream was running at a good clip, the springtails were being washed into the river behind my house, and there was a trail of springtails floating down the river as far as I could see!
While the larger, more common insects disappear when the weather turns cold, a little patience, a good eye and a magnifying glass will reveal one of the most abundant and unusual insects our winters have to offer.
Editor's note: Many scientists no longer classify springtails as insects; however, there is no consensus on where to place them. For the purposes of us non-scientists, we can just call them insect-like arthropods.