If you have gone for a walk recently and paused at admiring the fall colors to glance down, you might have noticed brown and black caterpillars migrating across roads. The woolly bear caterpillars (Pyrractea isabella) that we see crossing the road this time of year are actually the second brood and will overwinter in their caterpillar stage after feasting on late-blooming flowers like asters and sunflowers.
When you attempt to pick up the caterpillar while it is enroute to find the best hibernating spot, it will curl up tightly and the stiff hairs make it difficult to hold onto.
The lore of the woolly bear indicates the type of winter we will have by the size of the black portion of the bands on the caterpillar. The larger the black on the caterpillar, the harsher the winter, and the smaller the black bands, the milder the winter.
In the case of the woolly bear caterpillars that I found the other weekend, the black bands mostly started off larger by the head and smaller by the end, indicating that our winter will start off harshly but end mildly.
The reason for the discrepancy between the black and brown patterns of the caterpillars is actually more scientific and has to do with the stage of the caterpillar’s life cycle since the brown section gets larger with every molt the caterpillar makes.
In the case of caterpillars that are all brown or all black, they are simply different species of tiger moths in their larval stage.