12 April 2009

Woolly bear metaphorphosis - an easy project to do at home

One of Savannah's recent "science projects" is to observe the woolly bear caterpillar (Pyrrharctia isabella) turn into an Isabella Tiger Moth. Woolly bear caterpillars are especially common in New England during the fall and spring months and there old tales about how long winter will be based on the length of their brown and black stripes (although this really correlates to their age and growth before winter hibernation). Even though they hibernate all winter, come spring, they are hungry little buggers requiring a fresh supply of grass or leafy greens to eat everyday before spinning their cocoons. One nice thing about woolly bears is that they are rarely a nuisance to gardeners, preferring wild plants to cultivated ones. This is an easy project to do at home or school to enrich children's lives and understanding of the life cycles of animals.

We "captured" a woolly bear on one of our recent nature walks and brought it home. It resided in a clean applesauce jar with a foil lid that had many holes poked into it for circulation. We added a single strong twig, which is important for it to be able to climb and attach its cocoon to, and fed it either fresh grass clippings every day or fresh lettuce leaves every other day (the lettuce leaves usually last longer than the grass). I also put 1-2 drops of water in every two days but it's important to not have a wet jar and the lettuce and grass should provide enough moisture anyway. Every day for a week we cleaned out the old greens and put in the new greens for the woolly bear.

Today, the woolly bear climbed the twig and we watched it spin its cocoon throughout the day.

Here the woolly bear is beginning to spin its cocoon. You can still see through the threads to make out the whole caterpillar at the top of the twig.

I tried to get a close-up of this but my widest angle lens is only an 18-55. Now I know what to ask for for my next birthday...

Here the woolly bear has almost completed its cocoon and looks as though it is covered in fur. Now all we have to do is wait for 2-3 weeks for signs of the Isabella Tiger Moth to emerge. We'll release it outdoors as soon as it hatches but very gently, after its wings are unfurling and dry enough.

Additional tips:
  • Do not touch or move the jar when the caterpillar is spinning its cocoon - any vibration disrupts the process.
  • After the caterpillar has spun its cocoon, wait 1-2 days, then remove any leftover leaves or grasses so they don't rot.
  • Keep the jar in the coolest part of the house - a window sill of a cold room maybe, or on a covered porch where it won't get wet, so the caterpillar gets used to the regular outdoor temperature. If it emerges too soon due to perceived warmth, it may not have a food source in bloom yet.
  • If your caterpillar isn't thriving, release it outdoors.

Here are two more resources on woolly bears: general woolly bear info and raising woolly bears, with scientific info.

Some recommend capturing woolly bears in the fall as opposed to the spring. I find that woolly bears are just as easy to find in the spring so we take this shortcut instead of feeding and caring for them all through the fall and spring. I hope you have fun with your woolly bear project!

No comments: