Garden Corner – Woolly Bears

Kelly Jackson
Christian County Extension Office

Woolly Bears

In the coming weeks you should start noticing more and more woolly bear caterpillars actively seeking shelter for the coming winter. Quite possibly the most famous of all caterpillars, or at least well-know, is this bristly fellow because of his believed ability to predict the weather.

Woolly bear caterpillars are the larva or caterpillar stage of medium-sized tiger moths. The best-know of the woolly bears is called the Banded Woolly Bear. It is black on both ends and reddish-brown in the middle. Its adult stage is called the Isabella Tiger Moth. Other species of woolly bears include the Yellow Bear Caterpillar which matures to the Virginia Tiger Moth and the Giant Leopard Moth caterpillar which matures to a moth of the same name.

The Banded Woolly Bear caterpillar is about 2 inches long and although primarily orange and black, their color can sometimes vary from light tan for orange or dark brown for black. By the time we notice these guys in the fall we are actually seeing the ‘grandchildren’ (so to speak) of the woolly bears that spent last winter under some leaf litter, loose bark of a fallen log, or some other sheltered location. Two generations came and went this year largely unnoticed. They feed mostly on herbaceous plants like violets, clover, dandelion, occasionally wild grasses and on rare occasions maple and birch leaves. The adult moth eats nothing only surviving long enough to mate and lay eggs. Eggs are laid on the underside of leaves on trees, shrubs or weeds. The one you see today seeking shelter for winter is uniquely equipped with natural antifreeze inside its body that keeps it warm. Some reports indicate that the woolly bear can survive -90 degrees and has been known to survive an entire winter completely frozen in ice. Sounds pretty amazing!

Less than amazing unfortunately are their meteorological abilities. The classic belief being if the orange middle band is narrow then the winter will be cold; if it is wide it will be warm. Research has found this predictive method untrue. One study measured the average differences in band width over many years but failed to find a correlation to the upcoming weather. Instead the band widths relate to how long the caterpillars have been feeding and the moisture levels in the area where they developed. However, entomologists at the University of Massachusetts have found one weather link to the woolly bear. They say the orange band width of the caterpillar is a measurement of its age. The longer the caterpillar lives, the more orange hairs it will have and that is dependent on how soon it can begin feeding on plants in the spring. So, band width does relate to how long winter last but for the previous year, not the coming year. The wider orange band is indicating that the caterpillar went through a warmer winter than those with narrow orange bands. (Of course, we also went through last winter and already know what it was like.) Plus, the little woolly bears seeking shelter now are 2 generations removed from that weather-reporting caterpillar and will be bundled up and asleep before winter even arrives this year.

If this myth busting moment leaves you disheartened, remember don’t blame the woolly bear; people, not caterpillars, started this legend. The woolly bear could really care less.