White Tiger Moth – Either Fall Webworm or Virginian Tiger Moth

2015 July 15

Sam and Rosie found this white moth upstairs on December 24, 2014. At first I thought it was the adult form of the fall webworm. While one doesn’t normally see these in December (the adults come out in the spring), I remembered that the girls had been keeping webworms as pets back in September, and perhaps one of them had escaped to pupate in the house. But then I remembered the yellow woollybear caterpillar that Sandy found last fall, and I realized that I didn’t remember what I did with it. Did I turn it loose, or did it get put in a jar to pupate?. And given that it is plausible for it to be either of those, which one is it?

On the one hand, the Fall Webworm moth, Hyphantria cunea, is extremely common, and is probably our most common large, white moth. The local ones tend to have pure white wings, but they sometimes have spots.

On the other hand, the abdomen of this specimen is slightly colored, as we can see here after I got it to spread its wings enough to show what was underneath (and the fall webworm moths evidently tend to have practically pure white abdomens)

And there are just a few dark spots on the wings.

Both of these traits are more characteristic of the Virginian Tiger Moth, Spilosoma virginica, so it is looking more likely that this is from the yellow woollybear than from hypothetical pet webworms.

I really need to use a better indexing system for raising caterpillars. It isn’t so bad when I only have one or two, but more than that and it gets really easy to forget just what I’m rearing around here.

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