Sigmoid Prominent

2011 June 4

On occasion, we leave the front porch light on during the night, and then go out in the morning to see what was attracted to it. This is one of the moths that came on August 1, 2010. I was particularly struck by its bulging forelegs that it stuck out in front, as if it were prostrating itself:

This, combined with the way that it holds its wings and the upturned, tufted abdomen tip would seem to be pretty distinctive. But, it turns out that there are a number of not-very-closely-related moth families that have this same general shape, so I initially mistakenly thought that it was one of the Hypoptinae (a family of moths with wood-boring caterpillars).

When I posted it to BugGuide, I was quickly put straight by Ken Wolgemuth and Bob Patterson: it is actually a Sigmoid Prominent, Clostera albosigma. The “sigmoid” in the name refers to the s-shaped white mark on the rear part of the wings.

Sigmoid prominents are a generally northerly species, not too rare (although I was apparently the first person to post one to BugGuide from Michigan). Their preferred foodplants are poplar, aspen, and willow, all of which are very common around here (there are aspen trees just uphill from the house, and a good-sized stand of poplar off to the north a few hundred yards). The larvae are supposed to live in colonies and build tents kind of the way that tent caterpillars do, although they probably aren’t as noticeable about it. Then again, I might have been seeing them all along and just assuming they were tent caterpillars.

This particular one was practically comatose in daylight. When I poked it, it kind of just fell over (although it did eventually rouse itself and fly off). The other four legs looked pretty much like you would expect a moth leg to look. I don’t really know what the benefit of the big, fluffy forelegs is. Maybe it helps break up the outline of the head when it roosts on bark?

Like most moths, male Sigmoid Prominents have big, fluffy antennae. This particular individual has small, nondescript antenna, which are mostly hidden in the body fuzz (I think that the tip is visible pointing down to the left, but that could just be a foot). So, this looks like a female.

She was probably just sitting there, emitting scents from her upturned abdomen tip, and waiting for a male to smell her and come calling. The male’s big fluffy antennae are fantastically sensitive to the specific scent she emits, so this is a very efficient way for him to find her, particularly in the dark. As long as he doesn’t get eaten by a bat while flying around sniffing for her, they can mate and then she can flutter off to find an aspen tree and lay her eggs.

5 Responses
  1. June 4, 2011

    Am I the ONLY person who thinks this looks VERY much like a burrito?

  2. June 6, 2011

    Well, now that you mention it . . . yes. Yes it does. Although, if I had a burrito with a couple of muscular arms clawing out of one end, I think I’d be pretty leery about eating it.

  3. Della3 permalink
    July 31, 2011

    Burrito? No, no! Pic #3 shows a dog, running toward you, ears happily upturned, about to land a big kiss on your schnoz. Pic #5 is the head of a long-necked rabbit. Pic #1 is a malformed walrus whose front flippers got stuck on his head. O.K., that one’s a big stretch. I wanted to rename all five pictures, but ran out of ideas. Regardless, this little lady is just hilarious!

  4. barb quenzi permalink
    August 4, 2011

    we have yellow and black striped beetle-like insects in our house which when handled emit a nasty smell. Any at your house?

  5. August 5, 2011

    Barb: We’ve been seeing a fair number of these lately:

    Is that what you have? If it isn’t, maybe I could stop by and pick one up to photograph?

Comments are closed.