Tom Turpin
Professor of
Purdue University


Download the audio files or subscribe to our podcast.






Download the audio of On Six Legs: MP3, WMV.

Winter Not the Best of Times for Insects

Insects are cold-blooded animals. So are amphibians such as frogs and toads. Reptiles -- lizards, snakes and turtles -- are also cold blooded. Scientists classify these creatures as cold blooded because they cannot maintain their body temperature above the temperature of surrounding air.

Warm-blooded animals such as mammals and birds have the ability to keep body temperatures constant regardless of the air temperature. This is known as thermoregulation.

In humans, the normal body temperature is generally regarded as 98.7 degrees F. The normal temperature for a specific human isn't always exactly this temperature. Normal human temperatures range from 92 to 101 degrees F. Each human maintains his or her body temperature at the normal level, regardless of outside temperatures.

Cold-blooded animals can't do this and, consequently, don't do winter either. At least, you generally don't find cold-blooded creatures cavorting around during the winter months. In spite of the obvious inactivity of cold-blooded animals during frigid temperatures of winter, these animals do survive. Come springtime they will be back.

How do cold-blooded organisms survive winter? Generally survival is associated with one of two approaches. The first is hibernation where the animal's biological processes slow down to a minimum when temperatures dip. The other approach is known as diapause. Diapause is when the biological processes are suspended for a period of time long enough to bridge the cold period.

In the insect world both diapause and hibernation are mechanisms used to avoid the certain death that freezing temperatures bring to cold-blooded organisms. Some insects, such as many aphids and bagworms and that crop pest the corn rootworm lay eggs, are in diapause for the winter months. Other insects, including many ladybugs, some flies and a butterfly or two, spend the winter as a hibernating adult. Other insects while away the biting cold as pupae.

Much of the winter preparation by insects goes on as part of their normal life cycle and is unnoticed by human eyes. However, the month of October, when many of the teeming hordes of the insects of summer have buzzed their last, does bring one final onslaught of the six-legged kind.

The bugs of October are often directly related to wintering behavior. In fact, warm-blooded humans preparing to spend the winter in heated luxury of artificial structures frequently loathe the attempt of insects to share the buildings. Other humans don't fret as much about it. They like some insects; they just spend the winter in warmer climates. Of course, in such climates the warm-blooded insects are active during the winter months as well.

Asian beetles
Asian lady beetles

What are some of the more conspicuous insects of October? The Asian lady beetles that flock to sunny exposures of buildings such as our homes and schools and then proceed to find their way inside are among them. These lady beetles, as do most species of lady beetles, spend the winter hibernating as adult beetles in protected sites. Before houses were available, overwintering sites of lady beetles were associated with leaf litter in the forests or under rocks in the mountains. But these insect opportunists have found human structures to be suitable substitutes, much to the dismay of homeowners. Like all hibernating insects the lady beetles become active at higher temperatures and that results in the insects crawling around in our homes all winter long.

Other insects that can be seen preparing for winter during October include some of the aphids. Aphids are small soft-bodied insects that suck juices from plants and are sometimes called plant lice. In late fall, some aphid species produce winged forms that fly to host plants, where they will deposit eggs that will hatch in the springtime. Sometimes this flight involves millions of these small insects, which subsequently become the concern of humans who find aphids in theirs noses, mouths and eyes.

Another of the insect October crowd is that prognosticator of winter severity -- the wooly worm. Wooly worms are fuzzy larvae of moths. Such caterpillars are the wintering stage of the insect. These caterpillars crawl around on sunny October days seeking just the right site to spend the winter. Because they hibernate, each warm day induces them to crawl around. Such crawling makes them noticeable to people and no doubt has contributed to the wooly worms popularity as a weather predictor.

I don't put any stock on the reliability of wooly worms to predict how cold the upcoming winter will be. What I do know, though, is that wooly worms crawling around in October mean two things. One is that winter is on its way. The other is that the temperature that day is above the activity threshold for a cold-blooded insect.


Writer: Tom Turpin
Editor: Olivia Maddox