Tiger Moth Caterpillars | Wooly Bears


It’s interesting that this article came out when it did as yesterday I was noticing and thinking “why are there so many of these fuzzy caterpillars everywhere?”. Maybe they’ve always been this many this time of year but I’ve never noticed. Anyway, as Woods Houghton points out in the following article, this is just part of the natural life cycle of the tiger moth.

Article By Woods Houghton

I have been getting lots of calls wanting to know what is with the black fury caterpillars. Most of the ones I have seen are tiger moth larva; there are 63 species in New Mexico and 260 in the United States. Many species have ‘hairy’ caterpillars which are popularly known as woolly bears. Tiger moths get their name from their bold, contrasting coloration of the adult moth, which often includes gold and black strips much like those of the jungle cat. In various geometric patterns, red, white, and gray round out the colors of the tiger moth rainbow. You can usually identify adult tiger moths by color patterns alone; but, in general, these insects are also heavy bodied, slow, and deliberate fliers. When at rest, they fold their wings roof like over their bodies.

Many of the caterpillars and adults are active during the daytime. If disturbed, woolly bear caterpillars will roll into a tight spiral. Common folklore has it that the forthcoming severity of a winter can be predicted by the amount of black on the Isabella tiger moth’s caterpillar, the most familiar woolly bear in North America; however the relative width of the black band varies among instars, not according to weather. Isabella tiger moths (Pyrrharctia isabella) overwinter in the caterpillar stage. They can survive freezing at moderate subzero temperatures by producing a cryo-protectant chemical or insect antifreeze.

The life of a tiger moth begins when an adult moth lays an egg on the surface of a food plant. A few days later, the egg hatches and the larva begin feeding on plant food. Tiger moth larvae are distinctively hairy, which is a common characteristic of the family. Have you ever seen caterpillars covered by a dense coat of prickly hairs or by a sparser coat with long, hairy tufts concentrated at the head and posterior regions? They are almost always tiger moth larvae. Some people are very allergic to a chemical secreted onto the hairs or spines for self defense so you need to be careful when handling them. These caterpillars are really cool in that when bat ultrasonic locating sound waves hit them they emit a counter sound to confuse the bats.

Behaviorally, tiger moth larvae are of two types: they either enjoy company or live as hermits. Larvae of most species are solitary and rarely occur in large groups. For example, the banded woolly bear is often seen scurrying alone across roads in late summer and early autumn. The fall web worm is one of the more social of tiger moths. Large aggregations of fall web worm larvae live in web nests on their food plants–trees such as black walnut and elm. For the fall web worm, there is safety in numbers. If you find a fall web worm nest, gently tap the surface with a stick or your finger and watch what happens. The larvae immediately begin jerking their bodies back and forth in unison, presumably to dislodge predators or parasites. If you’re patient, you may see this show repeated when a real parasite lands on the nest.

Eddy County Extension Service, New Mexico State University is an equal opportunity/affirmative action employer and educator. All programs are available to everyone regardless of race, color, religion, sex, age, handicap, or national origin. New Mexico State University, U.S. Department of Agriculture, and the Eddy County Government Cooperating.

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