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How to Tell the Gender of a Banded Woolly Bear Caterpillar

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The elusive woolly bear caterpillar produces a natural antifreeze that allows them to hibernate in the winter; some even survive the winter completely frozen in an ice cube. It's as difficult to determine whether they're male or female as it is to find them once they've hidden for the winter. The male and female have some differences, but it's easier to distinguish the gender after they've transformed into full-grown Isabella tiger moths.

Lore of the Woolly Bear

Woolly bear caterpillars are in the Arctiidae family that transform into the Isabella tiger moth (Pyrrharctia isabella). They're familiar throughout the U.S., much of Mexico and part of Canada and are known for crossing roads and wandering in autumn in search of hibernation spots for the winter. They come out of hibernation in spring and feed for a brief period on a variety of herbaceous plants, shrubs and trees before spinning a cocoon from which they will emerge as moths after a month. Folklore suggests that the black bands of a woolly bear caterpillar can predict what kind of winter is coming.

Differences in Caterpillar's Appearance

Male and female woolly bear caterpillars are both black with a rusty red-orange band in the middle. They both have stiff, bristly hairs with a few longer, softer hairs sticking out. The only real discernible difference between them is that the male is generally around 2 inches long while the female is larger at 3 inches. Further identification is possible only through dissection.

Difference in Moth's Appearance

Female Isabella tiger moths are slightly larger than males. Their larger abdomens are necessary for carrying eggs. Both have a yellowish brown color with small spots on their wings. Their forewings are a light medium orange brown -- the same color as the head and thorax. The male's hind wings are a light yellowish orange with random black spots near the outer margin while the female's are more pinkish in color. The color of their abdomens usually matches the color of their hind wings.

Difference in Behavior

Neither male or female eat after their metamorphosis into adult moth form. The female moth extends a scent gland from her abdomen to release a mate-attracting scent into the air. The male will fly in a zigzag pattern at night, pick up the scent with his antennae and travel in her direction. After mating, the female will fly through the air dispersing her eggs on a number of hosts while the male finds other mating partners. Male moths are drawn to and rest near light whereas females typically do not.