Vagabond Crambus

2012 September 1

Here’s a moth that came to our porch light on August 1, 2010. In reality it was pretty tiny, maybe half an inch long, but that doesn’t mean I can’t blow it up to monstrous dimensions for your viewing pleasure:

It is a Snout Moth in the subfamily Crambinae. This is a pretty diverse subfamily of generally poorly-studied moths, the larvae tend to be stem-borers, root feeders, leaf tiers, and leaf miners. The common trend here is that the larvae are mostly hidden out of sight in whatever they are eating, and so the adults are pretty much all that will be seen.

The bushy, feather-duster-like things at the front are not antennae; the antennae are long, threadlike, and are running up its back. They seem to be just very bushy mouthparts, kind of like an out-of-control mustache.

For a long time, I wasn’t having much luck identifying this moth until I searched through the new “Peterson Field Guide to Moths of Eastern North America”. Among other things, the book has the nice feature that all of the pictures are on the right-hand side (meaning that if you just riffle through the pages, it is pretty easy to scan through looking for something vaguely similar, and then zero in). The moth is an excellent match for the Vagabond Crambus, Agriphila vulgivagella, with the key ID feature being the pronounced dots at the trailing edge of the wings.

The caterpillars eat a variety of grasses. Which wouldn’t be a problem, except that crops like wheat, rye, and other grains are grasses. So, in some areas, this moth can be a significant agricultural pest. Not so much around here, though, because most of the local agriculture is wood production, not field crops.

It is common to identify moths like this one as “micromoths”, which actually isn’t that much help as far as narrowing it down to a specific group. This basically means “one of the tens of thousands of species of nearly-unidentifiable tiny moths”, and it is often more an admission of futility than an actual classification. As organisms get smaller, the number of different species explodes[1] at the same time as the likelihood that anybody will actually examine and describe any given species plummets. I just got lucky with this one, because it is not only a very common species, but has been studied somewhat because of its agricultural pestiness.

[1] This relates a bit to my actual profession, which involves smashing rocks into powder. See, when you break rocks, you don’t get a bunch of uniformly-sized fragments. What you get is a distribution of sizes, with a few big pieces, more middle-sized pieces, and huge quantities of fines and dust particles. While the bigger pieces account for most of the mass, if you just count particles you find that the numbers of smaller particles completely swamp the number of larger particles. It turns out that this same principle applies throughout the natural world, ranging from stars and planets all the way down to grains of dust and ultimately single atoms or molecules: smaller things are more numerous than larger things, and usually follow what is called a log-normal distribution. This same principle applies to species: the smaller creatures are more common than the larger creatures, right up until you run up against some hard physical limitation that makes it impossible for them to live if they get any smaller. With arthropods, their cold-bloodedness and exoskeletal design makes it possible for them to continue getting more and more common as we work our way all the way down to microscopic sizes. And some moths are practically microscopic. As a result, it is relatively easy to get to know the few dozen to few hundred species of the big moths that occur in an area, but trying to be familiar with all the tens of thousands of sub-quarter-inch moths? That way lies madness.

3 Responses
  1. September 1, 2012

    Wow. I hadn’t realized that there were so many different moths (they all look the same to me). They look even more terrifying when you morph them as you have done here so that we understand that they are each monstrous creatures when seen intimately.

    This one seems less monstrous since you have given it that feather duster hinge to its door.
    It must be rather hard sweeping through bark and root and leaf with that thing in front of him. The rest of him (beyond the front parts) seem rather like a rolled up elongated wonton or cigarette. He is pretty if you just focus on the pattern of Morse code on his wings (I will assume this is a male because you have said his front mouth-parts resemble a mustache as I own I would not like to meet a female moth with this out of control appendage in front).

    If I look at him in a dispassionate way I could imagine him as a sort of scarab type ornament fit for pinning on the front of my shirt. But then you have blown him up way out of proportion. Micromoth sounds like the microfiber rags I use to clean house (rarely).

    I am glad you have a futile profession akin to mine (smashing stuff).
    Poets smash meaning into nothingness and like you (whatever it is you do –maybe hard labor at a penitentiary)—we get the same sort of messes—big going all the way down to small.
    We get huge quantities of junk that we put out on blogs so that folks who hate poets will hate them even more.

    But the moth.
    Yes, he is glassy eyed and incompetent looking and it is hard to believe such a tiny malignancy like this can cause metastasis in a grain field.
    But there you go.
    Just like poets, micromoths can cause disasters. Maybe we should get the same sort of appellation –Vagabond Crambus sounds way better than poet.

    I’d better stop yapping now and go back to Rabindranath Tagore who has just destroyed a world for my pleasure.

  2. September 1, 2012

    I think you’ve discovered a new species! Given the proliferation of such things, who’s to say you haven’t? Dub it Eisele’s Crambus and go have a beer!


  3. September 2, 2012

    Very interesting moth! Cool post…


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