White-Marked Tussock Moth Caterpillar and Adult Female

2017 December 17

Rosie found this caterpillar crawling on the side off our house on August 23, 2017.


It’s a White-Marked Tussock Moth caterpillar, Orgyia leucostigma, one of the more colorful caterpillars we have around here.


It is generally recommended not to handle these. The red glands on its back secrete defensive chemicals, and the hairs are kind of like mini-porcupine-quills and get stuck in your skin.


The long hairs around the head end in a little tuft of bristles, that probably are adapted to be as irritating as possible.


I had pictures of one of these way back in November 2008, that were actually taken by our friend Michelle, but this is the first time I actually got pictures myself.


Since this was pretty late in the summer, we figured it was quite likely that the caterpillar was crawling on our house because it was looking for a place to pupate. So, we put it in a jar, and sure enough, it cocooned up within a couple of days. The cocoon mainly consisted of its defensive hair bristles loosely tied together with silk. And, a bit over two weeks later, on September 13, 2017, this is what came out of the cocoon:


It turns out that female white-marked tussock moths have no wings, very little in the way of legs or mobility, probably no ability to eat, and are primarily devoted to being massive egg factories. She’s still standing on her cocoon in these two pictures, and showed every inclination to stay there.


If she had been outdoors, she would most likely never have moved from the cocoon, and just waited for a male (the males have wings and fly well) to come by and mate with her. As it was, we just transferred her outside to let her take up her post and wait.


These moths have astoundingly unfussy caterpillars, and evidently eat most anything green (although they do seem to prefer trees and shrubs). The eggs overwinter in a foamy mass laid by the female, and in the spring the caterpillars disperse. Sometimes they can become extremely common and defoliate trees, although I haven’t seen it happen around here.


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