The Isabella Tiger Moth:
Pyrrharctia isabella

Isabella Tiger Moth Caterpillar: Pyrrharctia isabella

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New! Caring for Woolly Bear Caterpillars

Woolly bear or fuzzy bear caterpillars are often found in the fall after they have left their foodplants in search of a dark and sheltered spot where they can hibernate as larvae for the winter. With springtime warmth, the woolly bear caterpillars again become active, feeding for a brief time and then fashioning cocoons out of silk and body hairs.

Tiger moths usually emerge from cocoons two to three weeks later.

Image of Pyrrharctia isabella moth courtesy of Anthony W. Thomas.

The Isabella Tiger Moth, (Pyrrharctia isabella, wingspan 4.0 - 5.5 cm) ranges throughout the entire North American continent.

Pyrrharctia isabella caterpillars are densely coated with black hairs of equal length with a girdle of the same length setae in red or orange. Two defensive postures are assumed when the larva is disturbed: 1) the woolly bear caterpillar curls up into a ball, or 2) the woolly bear caterpillar "runs" away as fast as it can. The head is small and black.

Woolly bear caterpillars feed on a variety of grasses and weeds including plantain, dandelion and nettles. Hibernation is usually over in northern portions of isabella's range in May. The caterpillars feed briefly, spin their cocoons and then emerge a few weeks later as adult moths.

There are usually at least two generations in the North and possibly three or more generations in the South. After dark, the female moth (larvae of females approach three inches in length) extends a scent gland from the tip of her abdomen. Night-flying males zigzag in their flights into the wind, pick up the airbourne scent with their antennae, and locate and mate with the calling female.

Upon separating, the male looks for another mate while the female begins her ovipositing flight under cover of darkness. Eggs are widely dispersed on a variety of hosts.

Male Pyrrharctia isabella moths come in to lights and rest with wings folded over their backs.

Pyrrharctia isabella caterpillars usually go unnoticed until fall when they seek out sheltered over-wintering sites. The longer the caterpillar has been feeding and the bigger it has grown, the narrower are the red-orange bands girdling its middle. Thus, the width of the banding is an indicator of the current or past season's growth rather than an indicator of the length of the upcoming winter.

Dormancy can be induced in larvae by chilling them and keeping them cool. Larvae have been known to survive an entire winter completely frozen in an ice cube. Warmth stimulates them, and in an active state they require food.

Many people write to me after finding these caterpillars in late fall and request information regarding their winter care. If the caterpillar is warmed, it will need food or it will starve after a few days. If you have inadvertently warmed an hibernating larva, the caterpillar can be rechilled and put back into cold storage until spring warmth brings fresh foliage. As long as the caterpilar is kept cold, it will remain dormant. I recommend putting the caterpilar in a small tupperware type container, lid on tight, no air holes or food. Mark the container and then put it in the refrigerator crisper where temps will be cold enough to keep larva dormant for the winter until food is available again in the spring. In the spring, as long as the rearing jar/container is kept clean and fresh foliage is supplied, the caterpillar will grow, spin its cocoon and then emerge as a moth. Enjoy the much larger, more spectacular moths depicted on the Saturniidae websites listed below.

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Woolly bear or fuzzy bear caterpillars come in a variety of colours and patterns, many of them quite striking!

Click on the hypertext (blue print) below to access info and images of various Tiger Moth adults and caterpillars:


Yellow Bear
Spilosama virginica
entire U.S, Can. and E. Mex....

Woolly Bear
Pyrrharctia isabella
entire U.S., Can., Mexico.......

Giant Leopard Moth
Ecpantheria scribonia
eastern 1/2 U.S. & Can.

Pale Tussock Moth
Halysidota tessellaris
eastern 1/2 U.S., Can. & Mex...

Hickory Tussock Moth
Lophocampa caryae
Mex., Sw. U.S. to Se. Can...

Spotted tussock Moth
Lophocampa maculata
E. 2/3 Can. U.S. border

Larval images are from Caterpillars of Eastern Forests courtesy of David Wagner.

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