Ribbed Cocoon-Maker Moth

2015 April 25

This moth from August 10, 2014 was only about 5 mm long (under a quarter of an inch), and was so tiny it could be mistaken for a bit of chaff. It looks like it has an eyespot at the tip of the wings, making it hard for a casual observer to tell which way it was facing. I’m not sure that this would make a lot of difference to a big predator, but maybe jumping spiders would be fooled?

I had thought at first that it was one of the leaf blotch miners in the family Gracillariidae, whose caterpillars burrow around inside of leaves eating the nutrient-rich middle, leaving the outer transparent layers to protect them from casual predators. Since leaves aren’t very thick, this leads to extremely small moths. However, I wasn’t entirely comfortable with this possible ID, because the posture of this moth was wrong (plus it had kind of a bushy “mop” of hair on its head)

So, I asked on BugGuide, where I was pointed instead to a related group of moths, the “Ribbed Cocoon-Makers”, family Bucculatricidae. Their tenative ID is Bucculatrix angustata, a little moth whose caterpillars make “trumpet-shaped mines”[1] in the leaves of goldenrod and aster (both of which are common local plants that I am quite familiar with), and fleabane[2] (which I hadn’t known the name of until just now, but which also looks like a plant that we have growing around here in some quantity).

[1] I think what they mean by “trumpet-shaped mines” is that the caterpillar starts out in the leaf at the point where the egg was laid, making a small-width mine where it starts feeding. Then, as it grows, it moves down the leaf and chews out a progressively wider channel in the leaf, so that by the time it pupates the mine starts narrow and then flares out.

[2] The information on fleabane is from the Minnesota Wildflowers site, which looks like a good resource for identifying flowers in the upper Midwest.

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