Woollybears and Winter
By : Timothy J. Gibb Ph.D.,Extension Entomologist Purdue University

Woollybears, also known as woollyworms, are the hairy caterpillars that can be seen scurrying across the road in front of cars at this time of year.  They are about 2 inches in length and vary in color from tans to dark brown or even a combination of both, depending on the species. The caterpillars usually remain unnoticed during most of the summer months even though they go through two generations.  The adult moth is usually white or yellow with black specks on its wings.  It lays eggs on the undersides of the leaves of trees, shrubs and weeds by the sides of the road where the caterpillars feed. 

In late summer or early fall, woollybears are almost comical in behavior as they are seen desperately inching their way across the road, as if they really have some place to go.  It is as if they have heard some caterpillar trumpet sounding "lights-out," triggering a frantic race across the road to find the perfect place in the soil in which to hibernate for the winter months.  Some species pass the winter in the cocoon stage while others wait until spring to form a cocoon.  Interestingly, woollybears can be seen going both directions, some going one way and some the opposite, often passing each other in the middle of the road.  It is apparent that neither one knows which side of the road offers the best sleeping spots, but that neither one wants to slow down to ask directions either (maybe they are all males). It is as if they have this little voice in their brain saying, “I have absolutely no idea where I am going, but I am going to be the first one to get there."  This observation leads me to conclude that woollybears aren’t really very smart.  They may provide motorists with good entertainment on an otherwise boring drive, but I doubt that they can be very smart, really.  Back and forth, back and forth, as fast as they can across a busy road!  I am developing similar doubts about people who believe that woollybears can predict the future.

Folklore has it that woollybear size and color can actually predict the severity of the approaching winter. One species in particular is banded with orange/brown in the middle and black at each end.  Folklore says that the coming winter will be cold IF the woollybear is darker than usual or has wider than usual black bands.  I know of no studies that have actually measured the variation in either color or band-width and compared them from one season to the next.  Nor can I even speculate as to why these little caterpillars would want or need to know the severity of the winter, considering that the ones that do not get run over during the fall will all be bundled up nice and snug in their little sleeping quarters by winter.  One thing that I am confident in predicting -- and you can mark this on your calendar -- is that whenever you see woollybears crossing the road in autumn, the next season is always going to be winter.  Furthermore, the winter months will be colder than the summer preceding.  All this I can predict by seeing woolly bears crossing the road, so in a sense woollybears can predict winter, I guess.  One more prediction that I can make is if the little inchers don’t keep moving really fast across the road, they are going to become a road schplatt when they get run over by my car, and then they will not have to worry about winter.  That is my prediction!

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