Frass Baskets

My research centers around urban ecosystems and invasive species. Typically, this means birds and non-native fruit, but I’ve done a fair amount of insect work and am always on the lookout for intriguing, exotic urban bugs. A few years ago, at a meeting of the Michigan Entomological Society, I saw a presentation about a moth introduced to North America around 2002. It’s been estimated that nearly 100 species of moths have been introduced on this continent from Great Britain alone. This particular moth, the Greenish-Yellow Sitochroa Moth, Sitochroa palealis, is also native to Great Britain, and its range extends to eastern Russia and south into North Africa; there are also records from the Far East.

Although my mind went a little numb listening to the details of the adult moth’s genitalia structure, I perked up when I heard that the larvae have a distinctive lifestyle. They feed on the flowers and seed heads of plants in the Umbelliferae (Apiaceae) family. In North America, the dominant host is Daucus carota, Queen Anne’s Lace, one of the most familiar non-native wildflowers in the U.S. This feeding habit accounts for the insect’s other common name, the Carrot Seed Moth.

The presenter at the meeting told us to look for larvae of Sitochroa palealis in the cup-shaped seed heads of Queen Anne’s Lace, as the moth was established in Michigan, as well as Illinois, Indiana, and Wisconsin. I spent the next two years peering into hundreds of seed heads, to no avail.

Eventually, my interest in finding the caterpillars waned, although I still looked at Queen Anne’s Lace seed heads out of force of habit. Last summer, I was walking through an old brownfield site along the Detroit River when I noticed a pile of frass – insect poop – in a seed head. I peeked inside, and there it was: a fat, speckled Sitochroa palealis larva. In fact, nearly every nearby Queen Anne’s Lace seed head acted as a basket of frass produced by a resident caterpillar. Often the caterpillar was hidden, but the frass was very conspicuous.

I never noticed any Sitochroa palealis adults at that site, but within a month I did photograph a rather boring-looking diurnal moth nectaring on Culver’s Root in my garden. It turned out to be the Carrot Seed Moth. It was quite fresh, and while I didn’t find any larvae in the neighborhood Queen Anne’s Lace, I now know what to look for.

And you do, too. In late summer, look for frass-holding Queen Anne’s Lace seed heads in the upper Midwest. In addition to the four states mentioned above, I’ve seen photos from Iowa, Pennsylvania, and Ontario. The Carrot Seed Moth could be coming to an old field near you!

Julie Craves

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5 Responses to “Frass Baskets”

  1. Julie Craves says:

    I just found more caterpillars at a few new sites the past weekend. Now is the time to look if you are interested!

  2. Justine says:

    I will definitely be keeping an eye out for this moth.

  3. “Frass basket”: I’m stealing that for a swearword substitute.

  4. holly says:

    We find these all the time in our Prairie at West MI Academy of Environmental Science (prek-12th grade in GR)and I have wondered what they are! Googled it and today we will teach the proper name! Fun stuff! They are all over the place…

  5. The contributors to Bugguide have reported this moth in the following states, as of July 2012: IL, IN, IO, MI, NY, ND, OH, ON, PA and WI.
    I will be looking for it in Pennsylvania. If they stick only to the non-native Queen-Anne’s-lace, it is fine with me. But I suspect, that sooner or later, they will find out that the native Apiaceae are just fine. Then there will be no stopping them. Sigh!
    Informative post, thanks.