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.

At least three still-downy Pied-billed Grebes were hanging out on Swan Lake waiting to be fed by parents. Also today, Connor found a green caterpillar crawling on the sidewalk. He brought it home and we were going to try to find it a food plant, but discovered it just wanted to bury itself in dirt, so we left it in a small bucket of dirt inside a rearing cage on the porch to see what might emerge.

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American Swordgrass Moth (Xylena nupera) caterpillar that Connor found crawling across a sidwalk. We discovered it wanted to bury itself in dirt, so we left it to it's own devices in a small bucket put inside a mesh rearing cage.

Three recently hatched Pied-billed Grebes loosely hanging together at the lower end of Swan Lake waiting to be fed by a parent.

Some of the moth coccoons formed by the various caterpillars the kids collected and kept fed.

I was a little surprised to find an active caterpillar on the branches of Sitka Alder (Alnus viridis) in February.

While down at Lincoln Street Beach the other day with Connor, I happened to notice this caterpillar crawling around on the branch of a shore-side Sitka Alder (Alnus viridis ssp sinuata). Later I found a couple of others, though I was unable to relocate the first one. They blend in to the branch quite well, so I was lucky to catch the first one moving. After knowing where to look and what to look for, I was able to find the others even when they were not moving.

I was aware that some species of moths and butterflies overwinter as caterpillars, but I have not previously found any here (not that I’ve been looking), nor did I expect there would be ones that are active in exposed locations through the winter. I’m making the assumption that these caterpillars have been active through the winter, as it hasn’t been so warm in recent days that I would expect things to decide winter is over. In any case, it seems likely that these caterpillars have a reasonable tolerance for freezing conditions. I found them on the ends of branches with no cover, so night-time temperatures on cold days would almost certainly get below freezing. I don’t think they could crawl back down the tree fast enough to take shelter in the dirt, but I could be wrong about that, I suppose.

There is some question in my mind about what these are eating. Given where I found them, it seems likely they are eating some combination of bark, buds, or developing catkins on the alders. It also seems possible, though unlikely, that they are just hanging out, but not eating, for the winter waiting for the leaves to emerge in the spring. If this is what they are doing, I see little advantage to being active at all over the winter, in fact, it seems like it would be a big disadvantage due to increased chance of death due to weather or predation. On a bud not too far from one of the caterpillars I found, I did notice a little bit of damage on a leaf bud. It could have been from a caterpillar chewing on it, but I’m not sure whether it was or not.

I was a little surprised to find an active caterpillar on the branches of Sitka Alder (Alnus viridis) in February.

I was a little surprised to find an active caterpillar on the branches of Sitka Alder (Alnus viridis) in February.