Woolly bears are caterpillars, black on the ends and brown in the middle.
They are supposed to predict the winter weather, but I have to look up which way the prediction works. Supposedly the more black and less brown, the harsher the winter will be.
According to the site below (1), some people call them woolly worms, but I've never heard this. Only woolly bear. And they are caterpillars of the Isabella tiger moth (Pyrrharctia isabella). The site says that they have 13 segments. They can come in nearly all black or nearly all brown.
In the fall of 1948, Dr. C. H. Curran, curator of insects at the American Museum of Natural History in New York City, took his wife 40 miles north of the city to Bear Mountain State Park to look at woolly bear caterpillars.
Dr. Curran collected as many caterpillars as he could in a day, determined the average number of reddish-brown segments, and forecast the coming winter weather through a reporter friend at The New York Herald Tribune.
Dr. Curran's experiment, which he continued over the next eight years, attempted to prove scientifically a weather rule of thumb that was as old as the hills around Bear Mountain. The resulting publicity made the woolly worm one of the most recognizable caterpillars in North America (alongside the monarch caterpillar and tomato hornworm). (1)
They are in the subfamily Arctiinae, of the family Erebidae, which contains around 11,000 species.
The most distinctive feature of the subfamily is a tymbal organ on the metathorax. This organ has membranes that are vibrated to produce ultrasonic sounds. They also have thoracic tympanal organs for hearing, a trait with a fairly broad distribution in the Lepidoptera, but the location and structure is distinctive to the subfamily. (2)