Forest Preserve District of Cook County, Illinois
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Hibernating Insects
Nature Bulletin No. 142   Febraury 14, 1948
Forest Preserve District of Cook County 
William N. Erickson, President
Roberts Mann, Supt. of Conservation

Insects pass through the winter in every stage of their lives: some kinds as eggs, some as larvae, some as pupae, some as nymphs, some as adults. Only a few, notably the Monarch butterfly, migrate southward. Of those that hibernate as adults, there are a few butterflies.

The Mourning Cloak butterfly spends the winter in barns or sheds or hollow trees, and on unusually warm winter days they may emerge and fly about -- good-sized butterflies with rusty black wings spotted with blue and bordered with pale yellow.

Ladybird beetles, or "Lady bugs", hibernate in big colonies under the loose bark of trees, in tree cavities, and in buildings. On warm winter days they may come out and crawl around. House flies, and the blow flies known as Bluebottles and Greenbottles, winter in cellars, attics and the crevices of buildings. If the temperature rises above 50 degrees, they will crawl or fly aimlessly about.

Many adult insects spend the winter underground. The May beetle, or "June bug", burrows down below the frost line. So do most kinds of ants. The young queen bumblebees lie dormant in burrows well below the ground surface. Many insects spend the winter as adults in or under rotting logs; some beneath the leaf mold or in the topsoil of woodlands; some among grass roots or in bunches of grass. Some beetles, for instance, get ready for hibernation by storing up fat, like bears. Other insects seem to be able to eliminate water from their bodies and can endure freezing temperatures for weeks at a time.

In general, uniformly cold winters with plenty of snow are easiest on insect life. Next best, are very mild winters with little or no freezing. Cold winters with occasional warm thawing days, and warm winters interrupted by severe cold spells, are both disastrous to many kinds of hibernating insects.

The snuggest bug is in a rug.

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