Winter Wondering: Where Have All the Bugs Gone?

February 15, 2005
When the groundhog named Punxsutawney Phil was pulled from his fake tree trunk in Pennsylvania on February 2, he
saw his shadow. According to legend, that means the winter blues are
sticking around.

So, what's the good news?

According to John Hanson Mitchell, an editor with the Massachusetts Audubon Society in Lincoln and author of the book A Field Guide to Your Own Backyard, insects in the winter lie so low they seem to have disappeared. Worry about bug bites can also wait for warmer weather.

But Mitchell said the six-legged critters are not completely gone. Instead, they're largely catching some shut eye before an active spring and summer. "If you look around in the winter, you can find a lot of insects—more than you'd think, especially on warm, sunny days, even though there's snow on the ground," he said.

Insect Survival

Like lizards and snakes, insects are cold-blooded. Their body temperatures rise and fall with the mercury in the thermometer. When insects recognize that winter is coming, they get ready by employing different strategies, according to Mitchell.

Some insects, like the monarch butterfly, simply don't stick around to see the arrival of winter. Instead, they migrate to warmer climes, only to return in the spring.

Ants and termites survive the cold by moving into and huddling together in the deep reaches of their underground colonies that extend below the frost line. There, they feast on food they stored during the warmer months.

Most insects, however, fall into a sort of deep sleep and wait for warmer weather to arrive. This sleep is technically known as diapause, a period of little or no activity like the hibernation of some mammals.

According to Kenneth Holscher, an entomologist at Iowa State University in Ames, insects begin to get ready for their winter sleep when they notice the shrinking hours of daylight in the fall. That's when they start doing things like putting on extra layers of fat.

"They also reduce the amount of water inside them," he said. "Water freezes at a high temperature compared to other liquids, so they reduce the water and replace it with glycerol, which is similar to the antifreeze we put in our cars."

Many of the insects that go into diapause are eggs and pupae awaiting the arrival of spring and its bounty of food before hatching into adults, Holscher said.

Other insects survive by creating galls, Mitchell said. A gall is an abnormal swelling of plant tissue like a cancer growth. Insects cause such a growth by sucking on a plant. The growth forms around the insect, shielding it from the elements.

"If you take a magnifying glass and go for a walk in the woods—a second-growth area where there's a mix of trees and shrubs—and start looking at twigs and cattails, these eggs and galls are everywhere," Mitchell said.

Sun Worshipers

Holscher said some insects will come out of their winter hiding places on days when the temperature rises above a "magic" threshold of about 45 degrees Fahrenheit (7 degrees Celsius).

"The sun allows them to heat up and get active, but the minute it cools down again, they're not going to be active at all," he said.

According to Mitchell, among the more conspicuous sun-loving winter insects is a type of springtail known as the snow flea. The fleas gather by the thousands on the sunny sides of trees.

Springtails are tiny—they measure about an eighth of an inch (two millimeters) long—and are found in damp areas where they feed on fungi and decaying organic matter. Their name comes from an apparatus on the undersides of their abdomens that allows them to jump uncontrollably into the air.

"If you look at them carefully, you'll see them hopping around. They look like hopping pepper grains, and they are everywhere," Mitchell said.

Another spot to find insects basking in the winter sun is a dead or dying tree. There, soldier beetles and mourning cloak butterflies will come out from their holes, which they bored into the bark to shield them from the winter's chill.

Also, winter stoneflies can be seen slowly lumbering through the winter sky. Other stoneflies are dormant and found in rivers and streams, clinging to the undersides of rocks in the coldest months of the year. But winter stoneflies emerge to mate and lay eggs from January to April.

Most insects in the winter, however, are found burrowed under leaf litter or bored into the bark of a tree or surrounded by a protective shell like a cocoon or gall.

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