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Q&A: The Great Caterpillar Attack

Question: What is it with the all those caterpillars on Campus? Why are they only in oak trees? What is their name? Will they turn into butterflies? What kind? What is their life cycle?

Answer: The good news is that this event is so common at Stanford [it happens every Spring], that these little creatures have been thoroughly studied. Currently, they are mostly the larvae of the Western tussock moth. Because there are so many oak trees on Campus, especially in public areas, that's the location we notice the most. However, the Western tussock larvae also feed on liquidambers, hackberries, manzanitas and Douglas fir. Due to overcrowding, they descend in great numbers from the trees, looking for more space in which to feed and pupate. They turn, of course, into tussock moths, not butterflies. Both the Stanford News Service and Stanford Grounds have put up very informative web sites explaining in detail the lives of the little beasts. The News Service story is devoted entirely to the tussock moth.

The Grounds web sites go into detail about most of the small pests at Stanford, and one of them has a special focus on the Caterpillar Story.

The US Forest Service has a nice identification page which has lots of pictures of the mature moths. They have an average wing span of 31mm and are a rather unromantic brown. Given their rather functional appearance and messy life style, I doubt that they'll wind up in a children's story.

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