This is an old Farmers' Almanac urban legend, that actually turned into scientific research. As the Farmers Almanac put it, based on the pattern or color of the wooly caterpillar. You could predict how the upcoming winter would be
Sweater weather season is quickly approaching and this year we're going to need them because it's predicted to be a snowy and cold winter in Michigan. And we could see the first snowfall before the actual start of winter.