Canton Daily Ledger, IL
09-23-06
Master Gardener's Corner: Woolly bear caterpillars and weather predictions
By RHONDA J. FERREE/Unit Leader/University of Illinois Extension, Fulton
County
Have you noticed all the woolly bear caterpillars lately? While driving back from
meetings recently, I noticed numerous woolly bear caterpillars crossing the
roadway.
Woolly bear caterpillars are about 2 inches long and covered with stiff bristles.
They are black with a broad band of red-brown bristles around the middle. These
caterpillars are the larval stage of the isabella moth.
These caterpillars feed on mostly wild herbaceous plants such as lambsquarter.
Although they seldom attack desirable plants, if they strip the weeds of foliage,
they may move on to flowers and other landscape plants. Once they move onto
desired plants, they usually are too large to be effectively controlled. In some
cases, handpicking the larvae off of the plants may be an option, but in most
cases trying to control these caterpillars this late in the season is not reasonable.
According to superstition, the amount of black on the woolly bear's bristle coating
forecasts the severity of the coming winter. It is the relative proportions of the
black and reddish-brown portions of the caterpillar that are supposed to predict
the winter. The longer the black segments on the ends of the caterpillar, the
harsher the coming winter.
One of the problems with trying to forecast the winter using these insects is that
the tiger moth has similar caterpillars as its larval stage. Unfortunately, there are
about 260 species of the tiger moth and each species has a different color
variation. Plus the caterpillars shed their skins or molt six times before reaching
adult size, and their colors change with each molt.
According to Donald Lewis, Entomologist from Iowa State University, there is
some year-to-year variation in the amount of black hair on these caterpillars, but
the differences are caused by age and wetness. Older caterpillars have more
black than young ones, and caterpillars that fed and grew in an area where the
fall weather was wetter have more black hair than caterpillars from dry areas.
So why do the woolly bears cross the road? No one really knows why, but they
cross roads and paths on warm days in late fall. Some people even believe that
this can predict the weather. If they are going south, it is going to be a harsh
winter. If they are headed north, it will be a mild winter. I was driving east and
west, so I don't know what that means!
If you don't believe woolly bears can predict the weather, you might instead want
to look at pig spleens, groundhogs, hornets, persimmon seeds, or read what
"The Old Farmer's Almanac" says.
You can watch the weather forecasters using their high-tech equipment. Or, you
can just wait and see what winter has in store for us. I suggest that you enjoy a
beautiful fall day with a nice walk outside while you wait.