Can Woolly Caterpillars Really Predict Winter?

Can the bands on woolly caterpillars foretell the kind of winter that’s ahead?

Woolly caterpillars, aka “woolly worms”, “woolly bears” or “fuzzy bears” have been said to do just that. According to legend, the brown band across the middle of these fuzzy critters changes depending on the type of winter that’s ahead.

A thin band is believed by some to mean you’re in for a bad winter. A fatter band is thought to predict a mild winter. Others believe that especially “woolly” caterpillars foretell a harsh winter . It’s also been said that caterpillar’s bands correspond to parts of the winter season. That is, the winter season will be off to a very harsh start if the first band is dark, or the end of winter will be mild if the third band is lighter.

But is there any truth to this belief? Or is it just folklore?


Researchers say a woolly caterpillar’s bands don’t forecast the weather. Instead, the bands and colors relate to the insect’s age, diet, growth and species. Bigger caterpillars are narrower in the middle. Their coloring reflects their age and how many times they’ve molted – that is, shed their woolly “fur.” As they molt, they take on more of a reddish hue. And while they may look similar, not all woollies belong to the same species. There are, almost unbelievably, more than 250 varieties of woolly caterpillars.

These caterpillars are copious in the fall, when you’re more likely to see them. That’s because, as the winter sets in, woolly caterpillars get set to hibernate. Each caterpillar then freezes itself solid. Finally, when spring arrives, each woolly spins a cocoon and emerges a few weeks later as a tiger moth.

Credit: photochem_PA

Credit: photochem_PA

Woolly caterpillars are harmless to people…so watch your step!



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