Woolly bear caterpillars

Will we have a mild winter or a severe one? Many people look to the woolly bear caterpillars to give an early forecast. The fuzzy caterpillars have subdued coloring, typically with a band of reddish brown in the middle and black bands at either end. The fuzzy hair-like covering is setae, a bristle formed from a single epidural cell which and provides some protection to the soft body. More famous than their adult stage of the Isabella Tiger Moth (Pyrrharctia Isabella), the caterpillars are typically seen in the fall and spring, with the fall hatch being more noticeable as they seek places to overwinter. The caterpillars prefer a habitat in meadows or forest edges, where they find a diet of clovers, and other low-growing plants and maple and birch leaves. Woolly bears are not considered a threat to crops or ornamental plants and flowers.

There are traditional folk sayings that relate the woolly bear caterpillar to the severity of the winter or amount of snow. Current science does not support a relationship with the woolly bear’s coloring, size of bands or thickness of “hairs” with the severity of the winter. However, beginning in the late 1940’s Dr. Howard C. Curran, the insect curator of the American Museum of Natural History in New York, over eight years found an 80% correlation between the wooly bears’ band length and the harshness of the winter. The results helped perpetuate the folk myth. Dr. Curran, his wife and a group of friends made fall trips, collecting as many woolly bears as they could in a day, which was the annual sample. They were out to have fun, and called their group The Original Society of the Friends of the Wooly Bear. Dr. Curran measured the number of caterpillar segments covered by the middle brown band and came up with average numbers, which were 5.3 to 5.6 segments of the caterpillar’s 13 segment body during the eight years. Since the middle segment was considered large, the black ends were smaller. The results coincided with mild winters at the time.

Some locales hold festivals associated with the caterpillar. Banner Elk, NC, for example, has a Woolly Worm Festival each October, with a caterpillar race, festivities, and a winter forecast based on the color of the woolly bear’s 13 segments corresponding with the 13 weeks of winter. The darker the segments, the more snow predicted. Typically over 20,000 attend, with 1,000 caterpillar entries in the races for a $1000 prize. Other locales with woolly bear festivals include Vermillion, OH, Beattyville, KY, Lewisburg, PA and Lions Head, Ontario.

The woolly bear’s adult stage, the Isabella Tiger Moth, or Tiger Moth, is a medium-sized moth with about a two inch wingspan and tan-yellowish wings with black spots. The female Tiger Moths have pinkish colored under wings, while the males’ under wings are yellow to orange. Females deposit their eggs on plants, with two hatches per year in our area. The late summer hatch of larvae or caterpillars overwinters in that form. The caterpillars produce a natural substance that allows them to survive freezing. In northern climates they have been found to survive temperatures as low as – 90 F. In the spring the overwintered caterpillars eat and then pupate. In our area, early spring tiger moths mate and lay eggs for the first hatch of the 2 hatches that take place. Research has shown that as the caterpillars grow and mature, the middle band increases in size, while the black end bands are reduced in size. That still doesn’t detract from the fun of looking at the harmless, fuzzy bugs in the fall and making a prediction about the winter.

Article by FCFCDB

Nature Notes for 11/17/2013