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Where Do Bugs Go In the Winter?

by Beth Fetterly

One of the wonders of nature is the seemingly complete disappearance of insects once the temperature drops below freezing and the subsequent multitudes of insects swarming each summer. Where do insects go in the winter? Do they die? Hibernate? Migrate? Stay active? The answer is yes. Insects are the most diverse order of animals; therefore, as one might expect, they have diverse responses to the harsh conditions of winter: some die, some hibernate, and some are active. Many insects die during the winter. Adults spend the warm months looking for a mate, lay their eggs and then die. One such type of insect is the Mayfly, order Ephemeroptera, whose scientific name describes the ephemeral nature of the adult’s existence. These insects are active as adults for such a short period of time that they do not eat or even develop mouth parts. Mayflies, sometimes nicknamed “kissing bugs,” all hatch at the same time (often in May, as their common name indicates) and swarm in giant mating clouds near lights or over water. They then lay their eggs in the water, which hatch into aquatic larvae and remain active in the juvenile form, even under the ice, until the next May. Interestingly, the existence of mayfly nymphs in a body of water indicates relatively high quality water. Perhaps surprisingly, they are common in the Milwaukee River. Insect hibernation gets its own name: “diapause,” during which the insect’s metabolic rate remains just high enough to stay alive. Insects may burrow into the ground or a tree and remain inactive for the cold months. Some have high concentrations of “insect antifreeze” such as glycerol or ethylene glycol (the same chemical used in our cars) within their bodies to prevent their tissue from freezing. These compounds are known in scientific circles as cryoprotectants. Two common examples of insects that go through diapause are ladybug beetles (that common pesky invasive species is the Asian Clown Beetle) and Mourning Cloak Butterflies. Native Ladybug Beetles that many of us remember growing up with hibernate in trees and under leaf litter, whereas the Asian relatives will invade our homes in winter. Mourning Cloak Butterflies over-winter in trees and are usually the first butterflies out in spring. They are mostly black, with cream colored outer wing edges. If you can get close to one, you’ll also be able to see blue spots and a purple hue to their wings. While we usually think of birds as migrators, there are several insects that do the same. The most well known is the Monarch, which may fly up to 2,000 miles to avoid freezing. For proof of this flight, visit the Urban Ecology Center where we have record of two tagged monarchs who flew 1768 miles from Milwaukee to Mexico! Other species of insects that migrate include some of the angle-winged butterflies and green darner dragonflies. Finally, some insects remain active in winter. Honey bees, for example, cluster together in their hives, consume up to 30 pounds of honey, and produce heat by vibrating their wings. Another common active insect is the spring tail, or “snow flea.” They are not really fleas, as their common name might indicate, and do not bite. Their common name refers to their size and they way they hop like a flea. However, they do not use legs to jump but rather a spring-like tail called a “furcula.” The tail remains folded under its body, held in place by a hook, until the insect releases the hook. The released tail then slams the surface of the snow, sending the insect propelling through the air! On the next mild winter day, this is a sight worth finding. The comma-sized springtail can be found on the surface of snow, usually near trees, feeding on fungi and algae. Depending on the species (there are nearly 700 documented in North America), springtails use varying forms of “insect antifreeze” as well as heat radiating off the white snow onto their dark bodies and from nearby trees to withstand the cold. Although we often don’t see them, insects will always be near, even in winter!
by Beth Fetterly