Why So Many Wooly Bears?

If you find yourself asking this question lately, you are not alone.  This fall it is hard to take a step outside in central Vermont without finding a fuzzy caterpillar underfoot.  Attentive motorists may find themselves swerving to avoid road-crossing caterpillars.  And as the nights become cold, wooly bears are finding their way indoors.  So, why are there so many this year?

In 2006, Sandal Cate (recently retired NBNC educator) posed that question to Dick Dearborn, a retired Maine Forest Service scientist.  That year had been a big one for wooly bears, but it doesn’t rival this year’s numbers.  “Some insects like the Woolly Bear will often have a peak in their population,” said Dearborn, “Woolly Bear numbers increase to a high point about every ten years.”  This pattern, however, is not exact and it can be hard to predict exactly when and why these peaks occur.

Part of why people are seeing so many now has to do with their life cycle.  Wooly Bears are the larval (caterpillar) phase of the Isabella Tiger Moth.  Wooly Bears feed on a wide variety of plants, although are not considered a garden pest, even in years where they are abundant.  The caterpillars overwinter and can often be found wandering in the fall in search of a suitable place to spend the winter months.  Their thick, bristly hair makes them unpalatable to most predators, so they can wander out in the open without fear of being eaten.  They can remain active well into November, so as long as there isn’t snow on the ground, we can expect to continue seeing Wooly Bears as they wander about!

So, watch your step out there… and help a Wooly Bear across the road this fall!

p.s. Here are some unusual looking Wooly Bears that we've found at and around NBNC in the past.