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University of Illinois Extension

How Do Insects Survive Winter?

December 15, 2012

During the winter months, Sandra Mason, University of Illinois Extension Horticulturist, often gets many questions from homeowners and gardeners hoping that extremes in weather will reduce the number of their most hated insect foes. However, such hope is often unwarranted due to the insect's ability to adapt to many different weather-related challenges.

In order to survive winter, insects push the pause button, actually the diapause button. The definition of diapause (and coincidently also the definition of an evening spent watching TV) is "an inactive state of arrested development." The shorter daylight lengths of fall trigger insects to enter diapause. During diapause an insect's metabolic rate drops to one-tenth or less, so it can use stored body fat to survive winter. Also, many insects produce alcohols for antifreeze. Their bodies can supercool (reach temperatures below freezing) without forming cell-damaging ice.

Insects spend the winter in various life stages: egg, nymph, larvae, pupae, or adult. Many overwinter as eggs. Aphid eggs can be found in the bud scales of woody plants. Bagworms hang out as eggs inside this year's bags. Tent caterpillars spend the winter as egg masses on branches.

Many insects, such as mourning cloak butterflies and bean leaf beetles, spend the winter as adults in protected areas such as under loose tree bark and in fallen leaves. Native ladybugs overwinter in herds under fallen tree bark or firewood. Asian multicolored lady beetles look for a warm spot in our homes to wait for spring.

Other insects overwinter in the larval or immature stage. Turf feeding grubs overwinter deep in the soil as beetle larvae. European corn borers survive as full grown larvae. Others, such as cecropia moths and swallowtail butterflies, overwinter as pupae in cocoons or chrysalis.

In order for insects to continue to the next life stage, diapause has to be terminated. The "play button" is generally warm temperatures. However, it would be a deadly mistake for an insect to "wake up" too soon. Therefore, most insects do not come out of diapause unless a long period of cold precedes the warm temperatures.

Insects are certainly adaptive, but winter conditions can affect their survival. Cold temperatures, fluctuations in temperatures, how long cold temperatures continue, how protected the overwintering location is, and if any snow cover is available all affect an insect's survival.

Source: Sandra Mason, State Master Gardener Coordinator, slmason@illinois.edu

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