Monthly Mystery #17: A Mystery in Reverse

Normally with natural history mysteries, there is some unexplained object or pattern that I wonder about until I stumble across an answer in the literature, or failing that, I eventually manage to locate or raise the organism that is responsible.  But here is an example where I thought I knew what I had to begin with, but now that I’ve succeeded in raising the insect, I’m not sure what to make of it.

The inchworm and sawfly discussed in yesterday’s post were both incidental encounters during my survey of Nantucket’s galls and leaf mines.  One of the things I was specifically looking for last spring was the leaf mine of an eriocraniid moth.  This is something that can only be found in spring because the larvae mine in fresh, young leaves, then drop to the ground and overwinter.  Once abandoned, the mines soon shrivel up beyond recognition.

In the same area where I collected the sawfly and inchworm, I managed to find a number of eriocraniid mines in scrub oak leaves, with their characteristic squiggly frass:

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The identification was easy: just two eriocraniids occur in the Northeast; Dyseriocrania griseocapitella, which mines leaves of various oaks (although Quercus ilicifolia happens not to be among the documented hosts), and Eriocrania semipurpurella, which mines birch leaves.  I collected some leaves more for the challenge of rearing some larvae to adulthood than to confirm the ID.  I had tried and failed to rear the birch species the year before.

The next day, the larvae were already abandoning their mines, and they eagerly burrowed into the small jars of soil I offered them.

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Last week, I was excited to see that one of the moths had emerged.  It perched calmly on the rim of the jar while I got some photos.

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A few days later, a second one emerged.  I found that when I positioned the lens so that the wings were perfectly in focus, they appeared black, with only a hint of that beautiful purple iridescence.

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But here’s the thing: I simply can’t reconcile these moths with  Dyseriocrania griseocapitella (or Eriocrania semipurpurella, for that matter).  The antennae and the wing pattern and shape are completely different. Here’s the only individual of that species I’ve ever seen, photographed at a light in May 2012:

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So what’s going on here?  Have I found a species that is known from elsewhere in North America, or has been introduced from somewhere else in the world? Is it a Nantucket endemic?  The only other species known from the eastern US is Eriocraniella mediabulla, described in 1986.  It occurs in Georgia and the Gulf Coast states.  The leaf mines from which I reared these moths are a perfect match for D. griseocapitella and not E. mediabulla, based on the distinctions made in the description of the latter species.  The antennae and wings, however, look pretty good for E. mediabulla, based on the photo of a pinned specimen in the original description.  Examination of genitalia (by someone other than me) will be necessary to say for sure what these are.  In the meantime, I’m starting to question whether the moth in the last photo is really D. griseocapitella.  Its head and thorax aren’t nearly as hairy as in the other examples here.  Well, whatever.  That’s enough staring at these moths for one day.

About Charley Eiseman

I am a freelance naturalist, endlessly fascinated by the interconnections of all the living and nonliving things around me. I am the lead author of Tracks & Sign of Insects and Other Invertebrates (Stackpole Books, 2010), and continue to collect photographs and information on this subject. These days I am especially drawn to galls, leaf mines, and other plant-insect interactions.
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2 Responses to Monthly Mystery #17: A Mystery in Reverse

  1. cinda gaynor says:

    wondering if you are headed nantucket way soon? finding lots of galls on the rosa rugosa – a first for me in 30 years – and it appears to also be diminishing the plants – of course it was an extraordinary winter …. something niggling in the back of my brain about parasitic wasp and rosa multiflora – will save some for you – but come on out!

    • I will be on Nantucket at the end of July, but Julia (Blyth) will be there around May 15-20 for the bird-a-thon, so she could get the galls from you then. I found some stem galls on rosa rugosa in Sept. 2011 that I believe were Diplolepis spinosa, but it would be good to get adult wasps to confirm… and maybe what you’re finding is something different anyway. Get them into sealed containers as soon as you can; they could be emerging soon!

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