Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
2/18/02
Contacts:
Donald Lewis, Entomology, (515) 294-1101, drlewis@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Yard and Garden Column for the Week Beginning February 22, 2002
Battling Wintertime Insects
Donald Lewis
Professor
Entomology
Insects are cold-blooded. Their body temperature rises and falls with the environmental temperature. Insects are usually active when it is warm and inactive when it is cold.
So what about all those insects that we see flying, crawling or buzzing in the winter? There are several explanations, but the most common is that insects active during the winter have found a warm microhabitat.
Microhabitats can occur for many reasons but the two most responsible for wintertime insect activity are home furnaces and sunshine. Insects that wandered into your inner wall spaces or attic during the fall did so to remain concealed in a protected location and spend the winter in hibernation. The heat in your home warms the insect hiding places to above the minimum temperature and presto! Beetles, flies and other insects are on the move again.
Sunshine can accomplish the same thing and this winter has been a good example. We've had not only unseasonable temperatures but also an abundance of sunshine and an absence of snow cover. The sunshine on dark soil creates very warm microhabitats on the soil surface where clover mites and many other small critters live and crawl. The result has been an unusual number of midwinter calls from outdoor invaders. Unfortunately, the only practical management option is to smile and endure their presence as you vacuum them up for disposal.
Real winter insects
Asian lady beetles, box elder bugs, attic flies and clover mites are summertime bugs that are not normally active in the winter. There are other insects that do appear in the middle of winter. These are moderately uncommon, and you have to be in the right place at the right time to witness their peculiar appearance, but the show is worth the trouble.
The first of the true wintertime insects is the snow flea. The snow flea is not a flea at all. They are small black springtails. Springtails are harmless insects found in damp areas where they feed on fungi and decaying organic matter. They are named for the unique apparatus located on the underside of the abdomen that allows them to launch forward in an uncontrolled jump that may carry them distances up to 10 times the length of their tiny bodies. Springtails are very common and abundant but get little notice because of their small size and the habit of remaining concealed near their food supply.
An exception is the snow flea. Dense swarms containing millions of snow fleas may suddenly appear on snow on a sunny winter day. Their black bodies on white snow and the swarms of up to 500 individuals per square foot draw the attention of midwinter hikers and others near ponds or in moist woodlands and landscapes. Snow fleas are present all year but they go unnoticed until their peculiar brand of wintertime activity.
Only the lucky few will ever witness a snow flea swarm. The rest of us will have to be content to read the reports of others such as Henry David Thoreau who included comments about snow fleas in his journal in January 1860.
Winter Stoneflies
One group of important but unfamiliar insects is the stoneflies. These soft, drab, medium-sized insects live in rivers, streams and lakes. The immature stage is a nymph usually found clinging to the underside of submerged stones (hence the common name). After a year in the water, the nymphs transform to winged adults that fly near the water to mate and lay eggs. Stoneflies are indicators of water quality. They survive and thrive only in clean, unpolluted water.
Most stoneflies are in step with the rest of the insect world. They are active in the spring or summer and the winter is spent in the state of suspended animation called dormancy. The winter stoneflies are a remarkable exception. The adults emerge anytime from January to April, often crawling from icy water, or emerging through cracks in the ice to crawl on stream banks and lake shores. A few manage to fly at slow, lumbering speeds and end up considerable distances from the water.
Insects resuming activity in a warmed microhabitat is not very mysterious. How a few specialized species perform at cold temperatures is one of the challenges waiting for a thorough explanation. It is easy to theorize that winter emergence has the advantage of little competition and reduced numbers of natural enemies like birds, toads, snakes, other predators and parasites. It's a good trick if you can do it!
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