09 September 2016

Monocolor woolly bears ?

Earlier this week one of my neighbors stopped by to visit, and inquired as to whether I had seen any unusual Woolly Bear caterpillars.  She had recently walked a couple miles on a local bicycle path and had seen lots of them - all of a single color (black or brown, perhaps one white) rather than the archetypal black-brown-black banded pattern.

Regional (and national) folklore holds that the width of the central brown or orange band is predictive of the severity of the coming winter.   The National Weather Service offers the following guidelines:
According to folklore, the amount of black on the woolly bear in autumn varies proportionately with the severity of the coming winter in the locality where the caterpillar is found.  The longer the woolly bear's black bands, the longer, colder, snowier, and more severe the winter will be.  Similarly, the wider the middle brown band is associated with a milder upcoming winter.  The position of the longest dark bands supposedly indicates which part of winter will be coldest or hardest.  If the head end of the caterpillar is dark, the beginning of winter will be severe.  If the tail end is dark, the end of winter will be cold. In addition, the woolly bear caterpillar has 13 segments to its body, which traditional forecasters say correspond to the 13 weeks of winter.

As with most folklore, there are 2 other versions to this story.  The first one says that the woolly bear caterpillar's coat will indicate the upcoming winter's severity.  So, if its coat is very woolly, it will be a cold winter.  The final version deals with the woolly bear caterpillar's direction of travel of the worms.  It is said that woolly bear's crawling in a southerly direction are trying to escape the cold winter conditions of the north.  On the other hand, woolly bear's crawling on a northward path would indicate a mild winter.
So... a report of monocolored woolly bears has some serious implications.   Does it portend...
The onset of "end times" ?
A Donald Trump presidency ?
Some other catastrophe ?
Or, to hijack Steven Colbert's favorite meme...

Accordingly, I set off down that same bicycle/hiking path.  After about a mile I had encountered just one crossing the path (photo at top).  He/she is clearly bicolored, but not distinctly banded.  So, more research was in order. 

The Wikipedia page on Isabella Tiger Moths indicates that the "brown band grows with age."  I also found photos of yellow woolly bears (caterpillars of the Virginia Tiger Moth).  And, finally, this best answer:
The woolly bear caterpillar's coloring is based on how long caterpillar has been feeding, its age, and species.  The better the growing season is the bigger it will grow.  This results in narrower red-orange bands in its middle.  Thus, the width of the banding is an indicator of the current or past season's growth rather than an indicator of the severity of the upcoming winter.  Also, the coloring indicates the age of the woolly bear caterpillar.  The caterpillars shed their skins or molt six times before reaching adult size.  With each successive molt, their colors change, becoming less black and more reddish.  In addition, there are approximately 260 species of tiger moths (the adult of the woolly bear caterpillar) in North America, and each species has slightly different color patterns and hair coverings.  As a result, some of the color and hair variations that we see each fall are a result of these different species.
I could have done the research first, but then I would have missed out on a nice autumn hike.  You learn something every day.


  1. There's a redundancy in your speculative outcomes--a Trump victory could easily be the "end times".

  2. I saw a solid black one last week here in Virginia. The scientific explanation is good to know but the folklore is more fun!

  3. that does not look like an woolly bear caterpillar i have ever seen.



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