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Woolly Bears Wandering

3-15-16 woolly bear 119 Woolly bears (larvae of the Isabella tiger moth) are on the march again- several weeks before I have seen them in past years, no doubt due to the warm weather we’ve experienced lately. They are one of the few moths or butterflies that overwinter as caterpillars. In the fall, often around the time of the first frost in the Northeast, woolly bears are often seen crossing roads as they wander frenetically prior to hibernation. At this time their body produces a chemical called a cryoprotectant that acts like an anti-freeze which protects living tissue against damage from freezing and thawing. They remain curled up in a protected spot, such as in leaf litter or under loose bark, nearly frozen solid all winter. When spring arrives and the temperature reaches the high 40’s and 50’s they become active again, feed for a few days, and then pupate inside a cocoon made with their own bristles. Adult Isabella tiger moths emerge in about a month, anywhere between April and June, mate, and lay eggs. Within two weeks the eggs hatch. In New England a second generation of woolly bears will be produced and these are the larvae that overwinter. (In even colder regions, such as the Arctic, there isn’t enough time for woolly bear caterpillars to consume enough food to achieve adulthood within a year, so they spend several summers feeding, hibernating each winter, for up to 14 years.)

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8 responses

  1. Hi Mary,
    Are you saying that these caterpillars live for 14 years?
    – Hugh

    March 15, 2016 at 9:28 am

    • Only in the Arctic, apparently, and this is the oldest record. This information comes from a BBC documentary done in collaboration with Britain’s Open University. I must say I have no idea how this was documented!

      March 15, 2016 at 10:00 am

      • That’s crazy! It would be interesting to follow up on that. Great work, as always.

        March 15, 2016 at 10:42 am

  2. Marie

    Fourteen years! Realizing how little I know about the world I see every day is fascinating. I am excited about this journey.
    Thank you!

    March 15, 2016 at 10:02 am

  3. k

    I really like wooly bears and therefore, when they are on the move, I am the one whose car you see swerving on the road for no obvious reason. Don’t want to hit the caterpillars!!!

    March 15, 2016 at 10:41 am

  4. Love woolly bears! The illustrator in me is now imagining the appearance of a 14 year old woolly bear caterpillar living in the arctic… compared to a young, whipper snapper, yearling woolly bear… I HAVE to draw that. Thanks Mary! Such fascinating info as always!

    March 15, 2016 at 10:58 am

  5. Pretty remarkable life cycle in the Arctic!

    March 15, 2016 at 6:05 pm

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