As the old saying goes, “March comes in like a lion and goes out like a lamb.” During this transition, overwintering insects begin to reanimate. One insect that will soon regain mobility is the woolly bear, Pyrrharctia isabella Smith (Lepidoptera: Erebidae). The life cycle of this insect is complex, but if it is properly understood, then lepidopterists will have a much better chance of seeing one in the wild.
The woolly bear overwinters as a larva. As the temperature gets cooler, the woolly bear larva will bask in the sun, using its dark coloration to gather heat. When the autumnal temperatures drop too low for basking to be sufficient, woolly bears ensconce themselves in leafy detritus. Snowfall serves to further insulate the moth from biting winter winds. Woolly bears are further protected by the chemical glycerol, which is produced by their bodies to protect them from extreme cold. This chemical is found in some antifreeze brands, and can be used in cars. Through strategic selection of overwintering sites and the use of glycerol, the woolly bear can survive temperatures as low as -60 oF.
Their survival can be put at risk if they are brought out of dormancy by unseasonal warmth, because they stop producing the chemicals necessary to protect themselves. Therefore, if a woolly bear is encountered in the wintertime, it is recommended that nature enthusiasts leave it alone.