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Woolly Bear Caterpillars

At this time of the year one can often spot caterpillars scampering, or at least moving as quickly as a caterpillar can, across the hot asphalt as one walks or bikes down the road.  They can be exceptionally abundant on country roads bordered by soybean fields.  The caterpillars look like undulating cheese puffs making their way across the road.  These are woolly bear caterpillars and there are eight or more species in the U.S.  Woolly bears are the caterpillar stage of a medium sized moth known as tiger moths (Family Arctiidae).  The actual reason they are crossing the road is they are searching for a sheltered location, such as under the bark of a tree or under plant debris, where they can spend the winter as a caterpillar.  The caterpillars can actually be frozen solid and still survive because they produce a substance called a cryoprotectant that protects their tissues from damage.  In cold climates the caterpillars may even survive and overwinter for two or more years before they get large enough to pupate.  In spring, they will feed briefly before spinning a cocoon into which their hairs are incorporated and eventually become a moth. 

Two very common species in Ohio are the Banded Wooly Bear (Pyrrharctia Isabella) and the Yellow Wooly Bear (Spilosoma virginica).  The course hairs of the banded woolly bear are black at both ends and reddish-brown in the middle.  The adult is called the Isabella moth.  The yellow woolly bears are highly variable in color.  The fine hairs covering the body vary from beige or yellow to dark reddish-brown.  The adult is called the Virginian tiger moth.  There are two generations of caterpillars each year, the largest usually occurring in August-September.  The caterpillars chew large irregular holes in the foliage and the extent of the damage depends on the number of larvae and the size and aesthetic value of the plants.  Defoliation of soybeans is never an issue, while a few woolly bears on a young canna lily can make the plants look quite unsightly.

The banded woolly bear is the species that is often cited as predicting the severity of the coming winter.  It is claimed the longer the black portions at the end of the body the more severe will be the coming winter.  Research has debunked this legend by showing the amount of black varies with the age of the caterpillar and the moisture levels in the area where it developed. 

While handling woolly bears is no problem, people with sensitive skin may develop dermatitis.  The hairs of some other hairy caterpillars can cause a painful stinging reaction.  So it pays to leave most hairy caterpillars alone.  

For more information on home, lawn, indoor, or outdoor garden care and tips, as well as other garden topics, visit www.ohioline.com and click on the Yard and Garden link, or call the OSU Extension, Butler County, at (513) 887-3722, or in Middletown at (513) 424-5351, ext. #3722.

News Release provided by Don Eberwine.