How to Read a Woollybear Caterpillar (And What Does it Turn Into, Anyway?)

What is this Woollybear trying to 'tell' you? Taken with a phone.

The Woollybear (sometimes called 'woolly worm') caterpillar has a long history of being used as a way to predict the severity of the upcoming winter, but how does one go about 'reading' the caterpillar? Well, there are actually four ways to read the future depending on which folklore you subscribe to. First, a little history.

History
It's no secret that the weather is difficult to predict with any certainty for more than a few days in advance. Unless you are content with the George Carlin forecast, you'll want as many specifics as possible.

 For the ultimate forecast, skip to about 2:20.

While for most of us today, bad weather is usually, at worst, an annoyance, for our ancestors, it could be a matter of life and death, especially over the course of a season. North America was first settled by the British on the Atlantic Coast from Virginia all the way through New England. These areas were all subject to changeable weather, ranging from hot summers to brutally cold winters. It was the last season, winter, that could make or break a fledgling colony. Knowing this, early pioneers started looking for any way, no matter if it was scientific or not, to predict the weather.

Being in the outdoors a lot (and having no smartphones, Internet, or TV), early settlers noticed things in nature that people today never would. Sometime a long time ago, and probably after an unusually harsh or mild winter, someone (no name is ever mentioned) recalled seeing caterpillars with unusually wide or narrow bands the previous fall and got the idea that the width of the caterpillar's orange band had something to do with the (then) upcoming weather. This person then probably told his (or her) idea to some friends, who also remembered unusual patterns on the caterpillars the previous fall, and who then talked about this 'discovery' to others.

Sometime after that, caterpillars of the same pattern were seen again in the locality and the following winter's weather was observed to be similar as to the year's when the coincidence was first noticed. Following the repeat event, locals probably became convinced that the caterpillar was a winter weather forecaster and word of this 'discovery' spread from its origin. In the time before science became accessible to the masses, it's no wonder that this belief became deeply rooted in the culture of the early colonies.

Over time, people passed down this folk belief to succeeding generations, who took it with them as they moved West of the Appalachians. This is how things would stay for 300 or so years.

Science Gets Involved
It was in 1948 that Dr. Howard C. Curran, an entomologist and curator of insects at the American Museum of Natural History heard about this folklore and decided to put it up to scientific scrutiny. That fall, Curran headed to Bear Mountain in New York in order to observe the caterpillars' orange bands. The finding: over half of the caterpillars he measured had wider than average (he studied insects for a living, so he should know) orange bands. According to folklore, this meant a milder than average winter. As history would have it, the winter of 1948-49 was mild for the region. The story was later picked up by the New York Herald Tribune and the Woollybear and its associated folklore was made famous.

 As an afterward, Curran was apparently intrigued by his finding to the point that he spent the better part of a decade repeating his caterpillar study. Result: no definitive conclusion, but the folklore was quickly becoming entrenched with a wider audience thanks to the Tribune's original story.

So How Do You Read a Woollybear?
If you haven't already noticed, the prognosticating 'powers' of the Woollybear are all in its orange stripe's width. In the most general terms, a wide stripe means a mild winter while a narrow one foretells a severe one.

Not content with this general forecast, some people have gone even further in specifics by playing a caterpillar numbers game. Coincidentally, the Woollybear has 13 body segments, which coincides with the 13 weeks of winter (at least according how the self-constructed calendar we developed arbitrarily divides the year). That aside, this expanded lore goes as follows. Each segment of the caterpillar's body, starting at its head, marks a week of winter. Like with its more generalist forerunner, orange body segments represent mild weather and black ones cold weather. According to this belief, one can now forecast the winter weather down to the week. In brief, the location of the caterpillar's orange band represents when the warm weather will occur and the number of segments that are orange will tell how long it will last.

Last but not least, there are two other ways to predict the weather via Woollybear that have nothing to do with stripes. According to one belief, the bushier the caterpillar, the harsher the upcoming winter. The final folklore states that the caterpillar's direction of travel forecasts the winter, with a North-bound caterpillar signifying a mild winter and a South-bound caterpillar meaning that the insect is fleeing to a warmer region to avoid a harsh winter.

And What do They Turn Into, Anyway?
While many people in the American Northeast and into the Midwest have heard of the Woollybear, very few of these people know what it turns into. Short answer: an Isabella Tiger Moth.

Science Says?
And what of science? Well, as Dr. Curran found out first hand, there's no real correlation between Woollybears' stripes and the upcoming winter weather. If one wants to get really technical, this is a prime example of the fallacy post hoc ergo propter hoc, translated to English, "after this, therefore because of this" or, in layman's terms, a false causal reasoning wherein one connects two events that have nothing to do with each other.

On the other hand, there is now a very certain correlation between Woollybear folklore and fun, whether it be the famous annual Woollybear Festival in Vermilion, Ohio, a way to introduce kids to and get them out in nature, or as a way to hone one's macro photography skills.

Above photos taken with a Nikon D700 coupled with a 200f4 AI Micro Nikkor and 2x teleconverter.

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