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Woolly Bears and Winter

Oct 08, 2018

While all bears are preparing for the winter, it's the familiar fuzzy caterpillar known as the woolly bear that clearly signals that cold weather is just around the corner.

On sunny autumn days, woolly bear caterpillars cross roads and highways. But even before there were paved roads, people noticed the woolly bear migration. Woolly bears were the weather predictors of folklore.

As the days grow shorter and the nights grow cooler, most green plants stop growing. Woolly bears are leaf-eaters, and they are quick to notice the shortage of food. Since caterpillars can't migrate south, their only option is to find a protected place to spend the winter.

Hollow logs, piles of leaves, cracks in foundations and stacks of firewood are all good places to hide. Woolly bears cross roads in droves as they look for winter dens.

The thickness of their bristles were seen in folklore as a snow predictor.  However, they function less for warmth on woolly bear caterpillars and more for helping them to freeze over more controllably.  The brown to black ratio is more an indicator of their age and how long they've been feeding than mild or harsh winter predictions.  You can learn more in the video below.

The fall migration of woolly bear caterpillars still remains a reliable sign of impending weather.

From Woolly Bear Caterpillar to Isabella Tiger Moth

  • The caterpillars are herbivores that graze on vegetation. They, like many other moth caterpillars, can be parasitized by wasps that lay their eggs on them and eventually kill them.
  • Woolly bears are fuzzy with dense, stiff hairs. They are usually black on the ends of the body and rusty red or brownish in the middle.
  • When disturbed, they commonly roll up in a ball.
  • The Woolly Bear Caterpillar turns into the Isabella Tiger Moth.
  • There are about 60 species of tiger moths in Missouri.

To discover more about the woolly bear, visit MDC’s Field Guide.


Woolly Bear Caterpillar
Woolly Bear Caterpillar

MO DOC-2018-Oct Wk 2 Wooly Bears-MDOC1810-LF02.mp3

Discover Nature Notes Radio
Woolly Bear Caterpillars and Winter

Animal Fact Friday - Woolly Bear Caterpillar

Wildlife Prairie Park in Illinois dives into Woolly Bear Caterpillar Facts
Wildlife Prairie Park in Illinois dives into Woolly Bear Caterpillar Facts


Isabella Tiger Moth
Isabella Tiger Moth

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