Comox Valley Naturalists Society
Knowing Nature . . .
Woolly Bears Crawl in the Fall
October 13, 2006
Anyone out walking this month is sure to encounter a fuzzy caterpillar, with black at each end and an orange-brown band across the middle. Known as woolly bears, these curious caterpillars are sure to capture the attention of children, who are often more attentive to nature than we are.
Though familiar with these creatures since childhood, I knew nothing about their life cycle and habits. I had heard about the folklore connected with woolly bears. The width of the orange-brown band is known to predict the winter to come: if it is narrower than the black bands, it will be a severe winter. If it is broader than the black bands, the winter will be mild. Some claim that the woolly bear’s forecast is up to 80% accurate.
This is taken quite seriously in parts of the US. In fact, a woolly bear festival takes place every year in Vermilion, Ohio, reputed to be the largest one-day festival of that state. Festivities include a parade, woolly bear races, and an official analysis of the woolly bear’s forecast for the winter.
Though weather predicting has greatly enhanced the woolly bear’s popular appeal, scientists dismiss the connection between woolly bears and weather, saying that the width of the bands has more to do with moisture conditions during its development, and the age of the caterpillar.
Woolly bear caterpillars, or larvae, are active in the fall, feeding and looking for a sheltered place to hibernate. Generally, they feed on leaves of deciduous trees such as maple, alder and cottonwood. Some species eat ground vegetation such as dandelions, grasses and plantain. Solitary by nature, and never very abundant, these caterpillars do not cause any considerable damage to trees or gardens.
During winter they curl up into a ball in a well-protected spot, until warmer temperatures of spring trigger them to become active again. Woolly bears may be seen early in the spring, in February or March. After feeding for a time, they make a soft cocoon, using body hairs and silk produced by the salivary glands. The woolly bear completely metamorphoses within its cocoon, transforming from a caterpillar to an adult moth. The moth, which emerges later in the spring, is an inconspicuous dull orange, and receives far less attention than its showier caterpillar stage.
Both moths and butterflies belong to the order of insects known as Lepidoptera. Moths differ from butterflies in many ways. Generally (there are exceptions) they are dull coloured and fly only at night. Moths have thicker, furrier bodies than butterflies, with larger scales on the wings. They have feathery antennae, compared to the club-tipped antennae of butterflies. Moths rest with their wings spread to the side, whereas butterflies often rest with wings folded over their backs. Butterflies have an exposed, smooth pupa, known as a chrysalis, while moths pupate in a silky cocoon.
Interestingly, moths can hear ultrasonic sounds that humans can’t. Some scientists believe that this is an adaptation to help moths detect predators such as bats, which use sound to echolocate their prey. Dr James H. Fullard, of the University of Toronto, is conducting studies to understand the relationship between bats and the dogbane tiger moth, a relative of our woolly bears. It has been suggested that the moths make ultrasonic clicking sounds, which may confuse the bats.
Apart from avoiding predation, the adult moth’s purpose is to mate, lay eggs, and start the life cycle again. After the egg hatches, the caterpillar grows by a series of moults. The stages between the moults are called instars.
The mature caterpillar has a body with 13 segments. The first three segments have pairs of “true legs” with tiny claws. The next four segments have pairs of false legs, called prolegs, which are fleshy extensions from the side of the body. At the back end, there is a prop leg, which helps the caterpillar cling to a piece of vegetation while it rears up its body to feel which direction to take. An undulating motion moves the woolly bear forward, and they can move surprisingly quickly.
Hairs, called setae, grow from small tubercles on the body. Some people have an allergic reaction to the hairs, so handling should be avoided. If disturbed, woolly bears will play dead by curling up into a tight ball.
Woolly bears are members of the tiger moth family, or Arctiidae. Several species of tiger moths are found in our province. The most common is the banded woolly bear, (Pyrrharctia isabella), which has an orange-brown band through the middle and is black at each end. The adult moth of this species is called the Isabella moth. Recently, I’ve been noticing another attractive species in our area, known as the spotted tiger moth, or spotted tussock moth (Lophocampa maculata). This caterpillar shares the same colouration as the banded woolly bear, but has black spots along the length of the orange band, and distinctive white tufts.
I have walked by these colourful woolly bears without thinking much about them. But these creatures are more interesting, and more adept than I would have thought. They can hibernate, spin a silky cocoon, and metamorphose into a radically different looking adult. Who knows, perhaps they can even predict the weather.
Click on a link below to view the CVNS newspaper column.