One of the enduring folk tales that relates to insects is that you can forecast the winter weather by examining the woollybear caterpillars in the fall. The woollybear in question is not just any of the 8 or more species of fuzzy, bristly-haired, tiger moth caterpillars found in the U.S., but rather the banded woollybear, the caterpillar stage of the isabella moth, Pyrrharctia isabella.
The banded woollybear is densely covered with bristly hair that is black at both ends of the body and light reddish-brown in the middle. It is the relative proportions of the black and reddish-brown portions that are supposed to predict the winter. According to most legend-tellers, the longer the black segments on the ends of the woollybear, the harsher will be the coming winter.
There is some year-to-year variation in the amount of black hair on banded woollybears, but the differences are caused by age and wetness. Older caterpillars have more black than young ones and caterpillars that fed and grew in an area where the fall weather was wetter have more black hair than caterpillars from dry areas.
This article originally appeared in the November 11, 1994 issue, p. 152.