Last July, Connor found a caterpillar which we thought we might try to rear by finding whatever food it wanted it. It didn’t take too long to discover that what it really wanted to do was bury itself in dirt, so we put some dirt in one of the kids’ buckets and left it inside a rearing cage on the porch. I took pictures and posted on bugguide.net, but wasn’t able to get an identity for the caterpillar.
Over the ensuing weeks, it was tipped over at least a couple of times by accident or when the wind blew the cage over – I wasn’t sure if that might be a problem for the cocoon (or is it called something else underground?), but figured it didn’t hurt to leave it out there. I was guessing that it would overwinter and emerge in the spring, but one mid-September morning the kids came in and told me there was a moth in the rearing pen on the porch and Rowan asked if I had put one in there. I told her I hadn’t and asked what the moth looked like. They said it looked like a woodchip. This didn’t inspire me to think that they had actually seen a moth, but I went down and took a look. Sure enough, an adult had emerged. I posted a picture of the adult on bugguide.net and was able to get an identification (with a little bit of a mixup due to mislabeled plates in the Moths of Western North America book I have). It was an American Swordgrass Moth (Xylena nupera).
They are found across the continent in a latitude band that includes Northern California to Southeast Alaska (though perhaps tending a little more southerly in the interior?). Larvae apparently eat many different things, and they overwinter as adults. It seems like a mid-September emergence leaves quite a long time for the adult to hang around until laying eggs in the spring. I imagine they must need to eat until the weather gets cold and they find a sheltered spot to spend the winter months.
I’ve never seen a moth like this before, and don’t really have any idea how common they might be around here, but it certainly was fun to have the mystery of the caterpillar identity solve. We decided to let this one go after watching it for a couple days. We put it out on the covered deck. Rowan checked on it from time to time, and it wasn’t too long before it flew off.