Future Moth or Future Meterologist?
Posted on November 3, 2023
Often referred to as “woolly bears” or “woolly worms,” caterpillars like the one pictured here are most commonly seen in late fall as they search for a spot to overwinter. Once they find a suitable log or bunch of leaf litter, they hunker down. Woolly bears are especially good at adapting to severely freezing winter weather and can withstand temperatures as low as -90 degrees Fahrenheit.
How Do They Survive Such Freezing Temperatures?
These insects produce a compound called glycerol that functions as organic antifreeze. While the caterpillars’ bodies will eventually freeze no matter what, the glycerol helps prevent ice crystals from forming within their cells, effectively keeping them alive. When the weather warms, they feed briefly before spinning cocoons and pupating. Come late spring/early summer, they emerge as adult Isabella tiger moths. After all that incredible super-survival, adults only live one to two weeks and die shortly after mating and laying eggs.
Woolly Worms As Weathermen
Their survival skills alone are pretty impressive, but these caterpillars are famous for a different reason—some people think they predict the severity of the upcoming winter. The width of their alternating bands of rust and black are said to signal how intense the weather will be during different parts of the season. According to the folklore, more rust generally means a milder winter. Wider black bands on their heads forecast a rough start to winter, while wider black bands on their backsides signal a harsh finale.
Based on this “logic,” the caterpillar we found at Sugarwood Forest Preserve (the one pictured) is telling us that we’ll have a severe start to the season followed by mostly mild winter weather for the bulk of it. Judging by the narrow black posterior band, we’ll finish things up with one final bout of wicked weather. While that forecast is rather believable (especially given last Tuesday’s Halloween snow), this myth is easily debunked.
The Debunking
Woolly worms’ unique coloring is dependent on several factors: their age, how long they’ve been feeding, and how many times they’ve molted, to name a few. It’s also typical to find several woolly worms during the fall, and they don’t all look alike. Beyond that, some look-alike species are often confused for woolly worms, further polluting the predictions. Some look-alike species are entirely black, inspiring panic in those who infer that the worst winter in history is on its way. Other look-alike species appear entirely rust-colored, leaving diehard woolly worm watchers unprepared for the frigid temperatures to come.
Whatever you believe, remember that this is a Michigan winter we’re speculating about here... anything could happen.
