Why Did the Woolly Bear Cross the Road?

Fall brings with it the familiar and well-loved sight of woolly bear caterpillars crossing roadways and sidewalks. Looking like orange and black-banded bottle brushes, these 1-2 inch caterpillars dodge vehicles and bicycles to get to the other side.

With luck and time, these beloved caterpillars will transform into Isabella Tiger Moths, a yellowish-brown moth not nearly as cute as its immature form.


Woollys in Winter

Woolly bears are one of the few caterpillars to overwinter as caterpillars, risking freezing temperatures and predation to emerge in the spring. Quite simply, woolly bears crossing roadways are risking life and legs to find the perfect leaf litter, the perfect board, or the perfect pile of wood chips under which to hibernate. They need a spot sheltered from drying winds, a bit of moisture, and cover from predators.

When they find that spot, they curl up in a tight ball and settle in for a long winter. Their bristle hairs are a deterrent to predators (although raccoons have been observed brushing the hairs off and then eating these insect delicacies). The spiky ball shape makes the caterpillars slippery to predators. If you try to pick up a woolly bear in its hibernating pose, you may find it slips from your grasp.

Woolly Bear

Come Springtime

If a woolly bear survives a New England winter, it will emerge in the spring very hungry. At this time of year, you may see caterpillars wandering again as they search for food plants. The caterpillar eats for a short while and then spins a cocoon, made of bristle hairs held together with silk, in a protected spot under rocks or bark. In two weeks, an Isabella Tiger Moth emerges from the cocoon.

The cycle begins again when the female Isabella Tiger Moth lays clusters of eggs on a variety of hostplants. Favorites include dandelion, grass, meadowsweet, nettle, and more. Eggs hatch in 4-5 days, and the young caterpillars feed in groups, becoming solitary as they grow older. Over 3-4 weeks, the caterpillars undergo 6 molts, or skin sheddings, and it is the second generation each summer that will cross roads to find that perfect overwintering spot.

Fun Facts about Woolly Bears

  1. Woolly bears are very fast (for a caterpillar, at least). They can travel up to 4 feet per minute, which is roughly equivalent to .05 miles per hour.
  2. Contrary to folklore, the woolly bear is not an accurate weather forecaster. Does the width of its orange band predict the severity of the oncoming winter? No. Instead, each time the caterpillar sheds a skin, its orange band grows a bit larger. So, broader orange bands are most likely an indication of the age of the caterpillar, not of future winter weather.
  3. Banner Elk, North Carolina has been celebrating the Woolly Worm Festival since 1978. During the “Woolly Worm Race,” pet woolly bears race up a 3 foot long string. The winner becomes the official predictor of winter.

5 thoughts on “Why Did the Woolly Bear Cross the Road?

  1. Jean P

    I have observed many black and brown striped caterpillars crossing the bike path. They are not wolly. Could they be immature wolly bears caterpillars?

    1. Kristin

      Good question – life spans are tricky to calculate with creatures that go through so many stages, but we can say that the woolly bear that overwinters as a caterpillar “lives” for 8 months or more, although most of those months are spent in a frozen state. That overwintering caterpillar will awaken in the spring, eat a bit, and create a cocoon from which emerges the Isabella Tiger Moth who lives a brief (days to weeks) adult life and hopefully leaves behind fertile eggs to create the next generation.


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