Forest Preserve District of Cook County, Illinois
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Where Do They Go?
Nature Bulletin No. 726   October 5, 1963
Forest Preserve District of Cook County
Seymour Simon, President
Roberts Mann, Conservation Editor


Walking through the meadows, fields and prairies on a balmy autumn day we hear the chirps, trills, buzzing and humming of innumerable insects. Many kinds have been multiplying since spring until their populations are beyond comprehension.

Butterflies dance in the air and flutter from flower to flower. Bees are industriously gathering nectar and pollen. Scads of startled grasshoppers and crickets leap and scatter ahead of us. The ground is alive with myriads of ants, bugs, beetles, caterpillars and smaller forms of insect life. In the woodlands, great companies of insects creep down from trees to find winter homes in weeds or the litter and humus beneath fallen leave.

Inevitably there comes a night when the temperature drops much below the freezing point and the vegetation is thickly coated with frost. On the following day no insects are seen or heard. Where did they go.

The grasshoppers died. So did all but a few species of butterflies, moths, and the adults of many other kinds of insects whose young, however, pass through winter in the egg stage or hibernate as larvae, pupae, or nymphs. The ants huddle in their burrows. The honeybees huddle in their hives. The bumblebee queens and the queens of colonies of social wasps have crept into protected places where they hibernate until spring, but the males and workers died.

All of the male mosquitoes died. Fertilized females of the common house mosquito (Culex pipiens), and of the Anopheles mosquito which transmits malaria, congregated in cellars, catchbasins, hollow trees and other protected places where they hibernate. The woodland and floodwater mosquitoes winter over as eggs.

Housewives are unpleasantly familiar with the adults of insects which, seeking places to hibernate, manage to creep through cracks and invade our homes: houseflies, the bluebottle and greenbottle blowflies, wasps, lady beetles, and that harmless nuisance -- the boxelder bug.

A few species of butterflies and moths migrated southward earlier in autumn: notably the Monarch butterfly -- sometimes in vast flocks, sometimes as far as the West Indies -- and some of them, tattered and torn, return in spring to lay eggs on young milkweeds. Adult angle- winged butterflies, such as the Mourning Cloak and Red Admiral, hibernate in outbuildings or hollow trees and become torpid but, on balmy winter days, may emerge and flutter aimlessly about.

Some kinds of adult insects can endure long periods of extreme cold while hibernating if those periods are continuous -- not interrupted by warm thawing days -- and some, believe it or not, survive being frozen.

The Viceroy, the fritillaries, and the little skippers, are butterflies that hibernate as caterpillars. The swallowtails and the white cabbage butterfly are some of those that hibernate as pupae -- naked chrysalids not protected by cocoons.

Some of the moths --especially the tent caterpillar, bagworm, cankerworm, gypsy moth and other injurious kinds -- pass through winter as masses of eggs. The woolly bear caterpillar, larva of the Isabella tiger moth, is a familiar example of those which hibernate in the larval stage. The caterpillars of many kinds of moths, however, spin silken cocoons around them and change into pupae before winter comes. Most youngsters are familiar with and collect cocoons of the big silk moths -- the Cecropia, Promethea, Polyphemus and Luna species.

In winter, if you turn over a rotting log, you may find a mouse's nest, a torpid snake or a salamander, a woolly bear caterpillar curled up tightly, and the pupae of beetles or other insects. Please put the log back as it was.

You may learn far more about "Where Do They Go" from the Field Book of Animals in Winter, by Dr. Ann Morgan, published by G. P. Putnam's sons.

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