UD entomologist Brian Kunkel debunks notion that woolly bear caterpillars can forecast weather.

Native Delaware: Woolly bully

Don't bother examining woolly bear caterpillars for winter weather forecast


8:10 a.m., Oct. 26, 2012--Weather forecasters are predicting a wild winter for the Mid-Atlantic, a far cry from the mild, virtually snowless winter we had last year.

Woolly bear caterpillars (Pyrrharctia Isabella) are saying the same thing – by virtue of the narrow middle bands seen on their abdomens this autumn. The bands at the ends of this striped caterpillar are black and the one in the middle is red-brown or orange. According to folklore, the wider the middle stripe is, the milder the coming winter will be. If the middle band is narrow, we’re in for a harsh winter.

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University of Delaware entomologist Brian Kunkel is no fan of cold weather. Matter of fact, he despises it. But he’s not losing sleep over the woolly bear’s narrow middle band this season. He says that no studies have connected the black woolly’s markings with the severity of the upcoming winter. However, they may be an indication of conditions the previous summer.

“The woolly bear caterpillars that have been active this month were hatched from eggs this summer,” says Kunkel. “Some entomologists think that variations in the caterpillar’s markings from year to year reflect growing conditions during larval development. A hot, dry summer may result in a shorter middle band than if it was wet and chilly. But I have not seen any hard evidence to support this.”

Entomologists do agree that some of the band variation is linked to differences in species and larval stage. The black woolly molts six times during the summer and fall. Every time it sheds its skin, the size and color of the bands change a bit.

The woolly bear caterpillar, like most Delaware insect species, has been busy this month making final preparations for the winter ahead. According to Kunkel, the majority of insects found in the state overwinter here, rather than migrating south. Exceptions include monarch butterflies, which can travel up to 3,000 miles each fall to Mexico and other warm climes. Other Delaware butterflies that migrate include the red admiral, painted lady, question mark and cloudless sulphur.

If you’ve seen lots of black woolly bear caterpillars traveling across your driveway this month it’s because they’ve been searching for the best place to hunker down for the winter.

“Black woolly bear caterpillars don’t mosey around in October; they’re in a big hurry to find a warm winter home before it gets too cold,” says Kunkel.

The black woolly can travel at up to 4 feet per minute or about 0.045 miles per hour. That may not be fast by our standards but it makes them the Usain Bolt of the caterpillar world.

After their blistering sprints across our driveways and yards, they cozy up in the cavities of rocks or logs or under tree bark for the duration of the winter. Come spring, they arouse, spin a cocoon and emerge in late May as the Isabella tiger moth.

“Delaware’s insects overwinter in areas sheltered from environmental conditions,” notes Kunkel. “Woolly bears favor rocks, logs and tree barks; other insects may shelter in wood or brush piles, under trees and shrubs, in sheds or garages, under siding or behind the shutters on windows. Basically, any good spot where they are protected from exposure to the elements.”

Like the woolly bears, many insects overwinter in the larval stage. But praying mantids go through winter in the egg form, moths in the silkworm family live as pupae, and mourning cloak butterflies overwinter as adults. And although few other insects are active, the nymphs of dragonflies, mayflies and stoneflies feed and grow all winter to emerge as adults in early spring. They live in the waters of ponds and streams, often beneath ice.

Brrr! The nymphs’ living conditions makes the woolly bear’s snug quarters, under logs or tree bark, sound downright inviting.

Article by Margo McDonough

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