Winter Weather and Woolly Bears

Or How Not to Predict the Weather

As we are now into fall, many conversations involve talk about what kind of winter we might have. Everyone has a theory based on various things--satellite data to the Farmers' Almanac, caterpillars to pig spleens, and aching joints to hair thickness. 

The good old standby of the Farmers' Almanac predicts a colder winter with more snowfall than normal for North America this year. And how accurate is the Farmers Almanac? Well it depends on who you talk to. The people who sell the book, say their predictions have been 80% accurate. Otherwise, you can take any year or place and make the predictions work or not. Accuracy is in the eye of the beholder. I'd like to believe that they are going to be wrong this winter.

How about some of the other indicators? The woolly bear is another favored one. The woolly bear is a fuzzy black and brown caterpillar of the Isabella tiger moth. They are seen a lot during the fall as they move around looking for a protected place to spend the winter. It seems like forever that I've heard people talk about the woolly bear and its predictions about winter weather. I was never sure how that worked, but I assumed they looked at their fuzzy coat and if it were heavier than normal, that meant a harsher winter. Turns out, I was wrong.

The predictions are made based on the ratio of black to brown stripes on the worm. Most woolly bears have a black stripe on each end with a brown section in the middle. If the brown area is bigger than the black areas, then it is supposed to be a milder winter. And conversely, if the brown area is smaller than the black areas, it is supposed to be a harsher winter. And how accurate is this predictor? Well it depends on who you talk to. Some say it can't miss and others say that it is more accurate in telling if last winter was mild or harsh.

Dr. D. H. Curran, curator of insects at the American Museum of Natural History in New York City, actually studied the woolly bear and its weather predicting abilities starting in 1946. For eight years he counted whether each of the 13 segments of a woolly bear was black or brown. He averaged his counts and then predicted the weather for the upcoming winter based on the black/brown ratios. His results were 80% accurate. However, he discounted his studies saying that he knew his sample size was not very large. Other experiments have had varying outcomes, so once again accuracy is in the eye of the beholder.

But not to be deterred by previous results, I set out to see what our local woolly bears were going to tell me about the upcoming winter. However, I ran into a few problems. The first one was even though these little worms are supposed to be everywhere, I only found six of them over the course of  several days. Of these, two were black and brown striped, and four of them were entirely black. That was the next problem. What was I supposed to do with the black ones? No one talked about those in the studies I read. If I went strictly on the black/brown ratio, we are in for a horrible winter. So, I decided to leave the black ones out of the study and use only two data points. Those two had healthy brown stripes, so I predict that we are going to have a mild winter. Now how's that for making the numbers say just what you want?

So what kind of weather are we in for this winter? I'm not sure. I think I may just have to stick my hand out the window when the time comes to know for sure.

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Want to read more?

Description and history of Farmers' Almanac

The Old Farmers' Almanac predictions for 2013-2014 winter in North America

How accurate is the Farmers' Almanac?

 The Old Farmers' Almanac describing the woolly bear and how it predicts winter weather.

All about the woolly bear caterpillar

Why do woolly bears cross the road?

Locations of various woolly bear festivals

Predicting weather with a pig spleen