Woolly Bears of Winter

  Bob Moul

You can predict this time of year that the nights will start to get colder and the news will carry stories of Woolly Bear caterpillars and their predictions of the severity of the upcoming winter.  The more dark segments it has, the colder the winter will be the old-timers will tell you.  As an old-timer myself, I am not convinced.

Certainly Pyrrharctia isabella caterpillars deserve a lot of respect because of their rugged life.  They are found as far north as Alaska, and seem to enjoy the cold.  They come equipped with the stamina and chemistry necessary to survive winter weather like Garrison Keeler's old bachelor Norwegian farmers.

"(The woolly bear) literally freezes solid. First its heart stops beating, then its gut freezes, then its blood, followed by the rest of the body. It survives being frozen by producing a cryoprotectant in its tissues."  Wikipedia

To prepare for winter the caterpillar has to eat a lot.  It does this over several months in Missouri where the growing season is long.  In Alaska where the season is short, it may have to last through several winters, emerging from its frozen state to put on "a few more pounds" before the next prolonged freeze.  They have been known to survive up to 14 winters!

Pity the poor Isabella tiger moth that will emerge from the woolly bear caterpillar's future cocoon next spring.  Indeed, the Wikipedia article on P. isabella doesn't mention the moth beyond a picture.   The specimen above is a female with the typical red-orange hind wing.  The moth has a lot of work ahead of it, first finding a mate and then delivering its eggs, all over its short adult life span.  The egg has to be placed on the appropriate host plants such as asters, birches, clover, corn, elms, maples, and sunflowers.

  Bob Moul

The story of its survival over winter as well as its supposed forecasting skills is told in this interesting video from Science Friday.

The pictures above were taken by an excellent amateur nature photographer, Bob Moul.  He submitted many images to Bugguide.net and BAMONA, an example of the contributions of citizen scientists to our natural history.  He passed away in 2011.