Tuesday, October 24, 2017

Can Wooly Bear Caterpillars Predict Winter Weather?

wooly bearThe woolly bear caterpillar is the larval stage of the Isabella tiger moth, Pyrrharctia Isabella. The Isabella tiger moth overwinters in the larval stage. In the fall, caterpillars seek shelter under leaf litter or other protected places.  They eat mostly weeds, including dandelion, clover, and grasses. Woolly bears are relative speedsters in the caterpillar world, crawling at a neck-snapping .05 miles an hour, or about a mile a day.

The woolly bear caterpillar — with its distinct segments of black and reddish-brown — has the reputation of being able to forecast the coming winter weather. According to legend, the wider that middle brown section is, the milder the coming winter will be. Conversely, a narrow brown band is said to predict a colder, snowier winter. Among a group of woolly bears, the stripes can vary greatly, making their forecast difficult to confirm; the same group of eggs can even hatch into caterpillars of varying dark and light bands.

Dr. C.H. Curran, former curator of insects at the American Museum of Natural History in New York City, tested the woolly worms’ accuracy in the 1950s. Although his initial  surveys found an 80% accuracy rate for the woolly worms’ weather predictions, Dr. Curran gave up the study in 1955 after finding two groups of caterpillars living near each other that had vastly different predictions for the upcoming winter. Other researchers have not been able to replicate the success rate of Curran’s caterpillars.

Most scientists discount the folklore of woolly bear predictions. Many variables may contribute to changes in the caterpillar’s coloration, including larval stage, food availability, temperature or moisture during development, and age.

Mike Peters, an entomologist at the University of Massachusetts, says there could be a link between winter severity and the brown band of a woolly bear caterpillar. “There’s evidence,” he says, “that the number of brown hairs has to do with the age of the caterpillar — in other words, how late it got going in the spring. The [band] does say something about a heavy winter or an early spring. The only thing is … it’s telling you about the previous year.”


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Jim Muller is an avid Adirondack winter camper who publishes WinterCampers.com. The site features news, information and tips and tricks for winter campers, along with stories and photos from his own adventures.

Jim has recently been taking canoe trips around the ADKs, documenting his trips on www.jimmuller.com. Visit WinterCampers.com to find out more about the joys of winter camping.

6 Responses

  1. Charlie S says:

    I picked up one of these little fellers just yesterday at a customer’s house in Niskayuna. It was on their deck and so I took it to a leaf-littered woodlot nearby and placed it at the base of a maple tree. I’m always doing this…picking up bugs and placing them away from human harm. It’s the nature in me to do so. Even wee ants that I find in homes…I’ll scoot them onto a thin sheet of paper, take them outside and release them into the outside world.

    • Michelle N. says:

      Love bugs and insects. I do the same thing.

    • Suzanne says:

      I do this, too. A few years ago, when I went to have my morning bath, I discovered a big spider in lurking in the tub. I carefully picked him (or more likely her) up with a tissue and ushered the critter outside. Later on in the morning I went over to the kitchen to be greeted by my 90-year-old mother, who said “You didn’t kill my spider, did you? I’ve been feeding it flies!”

  2. Larry Roth says:

    Well, if a smaller brown stripe means a harder winter…


  3. Paul says:

    “Other researchers have not been able to replicate the success rate of Curran’s caterpillars.”

    Then the answer to the question posed in the title is – NO.

    It sounds like even he had negative data (the other group that had no accuracy). Just because you get a one off result from a small cohort means nothing scientifically.

  4. Mary Nantell Pearce says:

    There will be over 100,000 people at yhe Wooly Bear Festival in Vermillion, Ohio this year! 2018! We want to know about our winter. Only the Wooly Bear caterpillar knows. Thin brown band, challenging winter. Wide brown band , moderate winter. I like the fsct we do this. Fick Gofdard is responsible for the interest . All northern Ohio loves Dick! As for me, c’mon snowy winter. I love snow. ?Mary

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