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Why does the Woolly Bear, Isabella Tiger Moth, cross the road? A look into the Woolly Bear Caterpillar

Updated on October 21, 2014

Woolly Bear

Woolly Bear
Woolly Bear

What is the Woolly Bear?

The Woolly Bear whose proper name is Isabella Tiger Moth ((Pyrrharctia isabella), is a brown and black banded caterpillar which lives in colder regions including the Arctic. In the fall the Woolly Bear larva comes out of the egg and spends the winter in the caterpillar form. During the winter it freezes with the heart being first followed by various body parts including the blood. The reason the Woolly Bear survives is by using a process called cryopretectant in its body. Cryopretectant involves an anti-freeze like substance to protect a body from freezing damage. This is why, during the winter months when we find a Woolly Bear outside, the body is stiff and cold and seems to be dead but it isn't.

Once the warmer spring weather comes the Woolly Bear's body thaws and enter the Pupa stage; forms a protective shell or cocoon around itself as the Woolly Bear's transformation into the Isabella Tiger Moth happens. As soon as the Woolly Bear becomes a moth it then has only days to find itself a mate.

But one interesting fact about the Woolly Bears in the Arctic is they often have such a short time for the feeding before the Pupate stage that they must endure the freezing process over numerous winters. Some have been known to freeze over a period of 14 winters. So, during those colder days in late fall when you see a curled up hard Woolly Bear, don't think it is most likely frozen...waiting for it's time to shine!


Why does the Woolly Bear cross the road

As I take my daily walk in the fall I become a one-woman Woolly Bear preservation society. Countless woolly bears are crossing the road and I scoop up each one and bring it to the other side of the road. I've been told that the Woolly Bear should be taken to the side of the road in the direction it was travelling. But why do they cross, what is the reason?

There is no great design as they seem to scurry with great haste across our roadways. They are only trying to find a plane to spend the winter in their larva form. These places include under dead plant debris such as leaves, under dead logs. It is there they will curl up and slowly begin the freezing process during which they continue to live.

So to answer the age old question, Why Does the Woolly Bear Cross the Road? get to the other side!

Isabella Tiger Moth


What does the Woolly Bear become

The Woolly Bear is actually a larval form of the Isabella Tiger Moth (Pyrrharctia Isabella). The moth is of a medium-size having wings that are cream and yellow-orange colored. The wings are spotted with black spots. The Isabella isn't as dazzling as other moth species and it's larva, The Woolly Bear, definitely takes center stage.

The Woolly Bear is seen from as far north as southern Canada down through the United States and into northern Mexico.

Food for the Woolly Bear


The Woolly Bear's desired foods

A popular food from a Woolly Bear's perspective is Clover. But at the start of it's life, the Woolly Bear will devour the plant it is born on, where the female moth deposited her eggs. Some of the plants include trees such as aster, maple, and birch or a sunflower plant. The Woolly Bear wil also eat dandelions (what a great natural de-weeder on our lawns), herbs, weeds, nettles, and grass.

Woolly Bear

The Woolly Winter Forecaster

The Woolly Bear has thirteen distinct segments of short bristles of hair. This hair does not feel like wool but rather like a hair brush. These thirteen segments are either black or reddish-brown colors.

Legend has it that the Woolly Bear predicts the weather depending on how wide the middle reddish-brown section is; how many more of the middle segments are of the reddish-brown color. A mild winter will happen if the Woolly Bear has a wide reddish-brown band and a harsh winter will happen if the band of reddish-brown is narrow. Is this true?

Between the years of 1948 and 1956, the curator of insects at the American Museum of Natural History in New York City studied the Woolly Bears and the legend. In the fall Dr. Curran collected as many Woolly Bears as he could, counted the middle segments, then averaged the wide vs narrow band numbers. When the middle segments were wider the following winters were in fact milder.

Although this was not a controlled experiment the idea became popular with folks and the Woolly Bear has continued to be the unofficial winter forecaster.

Do You Believe?

Does the Woolly Bear predict a winter's severity?

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What is this?

All Black Woolly Bear!
All Black Woolly Bear!

All Black!! Oh No

We found today this large, very bristly Woolly Bear. He was much larger than others we have found and he was all black. As he moved across my daughter's hand the reddish-brown segments could be seen deep in between the black bristles. It was as if the joint of the segment had the reddish-brown color.


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    • MimiKat33 profile image

      MimiKat33 3 years ago from Northeastern NY State, USA

      I didn't find any information about that but feel free to comment if you do. I love these little creatures and call myself the one woman Save the Woolly person in the fall when they are all over the road I walk on :)

    • poetryman6969 profile image

      poetryman6969 3 years ago

      Cool article but I thought some of the more colorful ones were poisonous?