Isabella Tiger Moth (Woolly Bear)

The Isabella tiger moth belongs to the subfamily Arctiinae within the family Erebidae, the tiger and lichen moths, a group broadly known for hairy caterpillars and often boldly patterned adults. While the adult moth is relatively plain compared to many of its tiger moth relatives, its caterpillar, the banded woolly bear, is one of the most culturally recognized insect larvae in North America, tied to long-standing folk beliefs about predicting the severity of the coming winter based on the width of its color bands.

The species is widespread and hardy, ranging from northern Mexico into the Canadian Arctic, and it is notable among insects for its extreme cold tolerance, with the caterpillar able to survive being frozen solid during winter and thawing out again in spring to resume development.

• Adult moth: yellowish-orange to tawny-brown wings, sparsely dotted with small dark spots, and a stout, furry orange-tan body with a wingspan of roughly 38–55 mm.
• Caterpillar: densely covered in stiff bristly hairs (setae), with a broad reddish-brown or rust band in the middle and solid black bands at both ends.
• The width of the caterpillar's rust-colored middle band varies by individual and instar, the basis of its winter-forecasting folklore, though it is not a reliable indicator scientifically.
• Curls into a tight ball when disturbed, a common defensive posture among woolly bear caterpillars.
• Distinguished from the similar-looking giant leopard moth caterpillar, which is uniformly black with red bands only visible between segments.

Occurs across nearly all of North America, from Mexico through the United States and Canada into subarctic regions, tolerating an unusually broad range of climates. Found in open habitats including meadows, gardens, roadsides, and forest edges. Caterpillars are especially conspicuous in autumn as they wander in search of overwintering shelter, while adults fly mainly in late spring through summer.

Caterpillars are generalist feeders on a wide variety of low-growing plants, grasses, and weeds, causing negligible damage as individuals. In late autumn they seek sheltered spots such as leaf litter, bark crevices, or under logs to overwinter, tolerating freezing temperatures through natural antifreeze compounds in their tissues. Adults are nocturnal and, like many Arctiinae moths, are relatively unpalatable to some predators due to chemicals sequestered from larval food plants.

Eggs are laid in clusters on host plant leaves in summer and hatch into small caterpillars that feed and grow through several instars before autumn. The nearly full-grown caterpillar overwinters in a dormant, freeze-tolerant state, resuming feeding briefly in spring before spinning a cocoon incorporating its own bristly hairs and pupating. Adults emerge in late spring to summer to mate and lay eggs, with one or two generations occurring per year depending on latitude.