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Woolly Bear Caterpillar

by Stan Tekiela
© NatureSmart
November 21, 2010

Photo by Stan Tekiela©


It's funny how some things in nature are very familiar and well known. For example the robin. Stop just about anyone on the street and show them a robin and they can identify it correctly. The same can be said for the small black and orange Woolly Bear Caterpillar. Why this is, I'm not sure. So besides the name, what else do you know about this fuzzy caterpillar? I'll bet, not much.

There are a number of common names for this tiny critters--Banded Woolly Bear and Black-ended Bear are just a few. Called woolly because they are covered with a thick, uniform length fur like hair called setae. I have no clue where the bear part of the name comes from. However they are cute and fuzzy like a bear, perhaps that is how they got their name. They also come in many color forms such as tan or even white.

Many think that the woolly hair (setae) cause skin irritation or inflammation if touched. This is not true for the average person. However some people with extremely sensitive skin may have a slight reaction (dermatitis) if they handle the caterpillar. Speaking of handling, the woollies will play dead if picked up or disturbed. They curl up onto a ball and don't move until the danger passes. This is standard behavior for helpless critters such as the woolly.

Woollies are usually seen in late fall when the leaves are golden and the winds turn cold. They are often seen slowly crossing roads, trails and sidewalks. Why they wonder around at this time of year is not clearly understood because woollies can eat just about any kind of plant so they aren't looking for a food source. So why would they risk coming out into the open and being eaten by a bird or getting run over by a car? Just one more mystery that nature has for us that we won't be able to answer.

It is often said that you can predict the severity of the coming winter based on the width of the orange band on the woolly. The narrower the band forecasts colder winters. In fact, the band width is high variable during each stage of the Woolly Bears life. As the caterpillar grows it sheds its skin. Each stage is called an instar. Some of the black hairs are replaced with orange and the band grows wider with each instar. I think it goes without saying that Woolly Caterpillars are not capable of predicting any kind of weather, short term or long. In addition, the band width and even the color is highly variable with each individual caterpillar. The hatchling caterpillars from the same mother are highly variable indicating the band width is more a function of its genetics than anything else.

So what does a fuzzy woolly caterpillar turn into as an adult? The adult is the Isabella Tiger Moth. It is a small yellow to orange moth with tiny dark spots on the wings. It has a fuzzy orange head and small antennae. They are a fairly unremarkable moth that would most likely go unnoticed by the average person.

Throughout most of the eastern US the Woolly Bear lives in just about any habitat that include a variety of trees and other herbaceous plants. It occurs from Canada to Florida and west to Texas. In many areas it can be very common and seen by the hundreds and thousands. Two generations occur each summer with the second generation of caterpillars over-wintering as caterpillars. This is fairly unusual because most of our insects over-winter in the egg form. The woolly curls up in a ball under the leaf litter and survives by freezing. They do this by producing a cryoprotectant in its tissue that protects the individual cells in the body from damage during the freezing process. In spring it thaws out and continues to eat a little more before transforming into an adult moth and starts the entire process over again. Until next time...

Stan Tekiela is an author / naturalist and wildlife photographer who travels the US to study and photograph wildlife. He can be contacted via his web page at


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