Wild Profile: Meet the woolly bear caterpillar

By Nancy Bauer/Shutterstock

Fat, furry, and rumoured to be able to predict the weather: that’s the woolly bear caterpillar in a nutshell.

Rust-and-black banded woolly bears are the larvae of Isabella tiger moths. They’re born completely black. Their orange-brown middle sections appear as they get older and grow longer (up to 5 cm).

So how do these caterpillars foresee the future? Allegedly, a caterpillar with a wide rust-coloured midsection and narrow black bands at either end of its body forecasts a mild winter; a caterpillar with the opposite colouration predicts a long, harsh winter. In reality, the thickness of the caterpillar’s rust or black bands has to do with its age and growth rate. Each time a woolly bear moults, the rust-coloured portion of its body gets longer.

Woolly bears are most noticeable in fall, around the time that we’re hit with the first frosts. Look for them inching across roads and driveways, on their way to find a spot to overwinter in the leaf litter or under rocks and rotting logs. Look, but don’t touch—unless you’re willing to risk a rash. Woolly bears may appear fluffy, but their coats have tiny barbs at the tips that can break off and irritate your skin.

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