Winter Leafminers

Happy New Year! As I mentioned before, now that winter is upon us, I get to take a break from collecting and raising leafminers and focus on writing about them. At least, that was the plan. On December 25, while on a family walk in the woods behind my parents’ house, Julia plucked a sedge leaf and handed it to me for inspection. The leaf tip was dead and brown, but the rest was green. A short, narrow line extended from the dead area toward the base, and on close inspection there was a caterpillar inside:


The field of view in the above photo is 2 cm wide, and I have no idea how she spotted the mine. Since the larva was a dark reddish brown color, I wasn’t sure if it was alive. But when I got it home and started taking pictures, I could see that its head was moving from side to side from one picture to the next. I don’t know how long I will be able to keep the leaf green, but the larva is still alive and well. Below is a photo I took a few minutes ago:


The two photos are at different magnifications, but if you note how far the larva has moved past the little hole in the leaf that was right next to it in the first photo, you can see that it has been actively feeding over the past week. This is not a case of an insect hatching prematurely, being fooled by unseasonable warmth into believing that spring has arrived. Annette Braun reared several species of Cosmopterix and Elachista that begin mining sedge leaves in the fall, completing development in the spring. Obviously they go dormant when temperatures are below freezing, but on milder winter days they continue to nibble away.

I haven’t organized my chapter on sedge miners yet, so I won’t hazard a guess as to which species this is, but I’m confident it isn’t Cosmopterix clemensella, the sedge miner I’ve written about previously here. That species expels all its frass through a hole at the beginning of the mine, whereas you can see there is plenty of frass in this mine (the larva has definitely been returning to the linear portion to deposit its frass, though, in order to keep its feeding area clean). I suspect this is one of the many Elachista species, which are known as the “grass miner moths” (a great disservice to the species that feed on sedges and rushes). It may or may not be the same as this one I reared from a sedge in May 2012, which may or may not be E. cucullata:


The immature stages of most Elachista species have not yet been found, so there is no particular reason to assume that this is one of  the species that has been reared from sedges before. And the microlepidopterist to whom I sent the above moth has warned me that the adults are very difficult to identify, despite the extensive work Lauri Kaila has done to revise the North American species. So there is no particular reason to assume that rearing this larva to an adult moth will get me any closer to being able to put a name on it. But I carry on, with the hope that someone will get it all sorted out someday.

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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6 Responses to Winter Leafminers

  1. Sue Cloutier says:

    Great mysteries in nearby places… enough to keep you exploring for a lifetime. Thank you for sharing and have a great new year ahead.

  2. John Coffman says:

    How would it have been to repot the plant?

  3. John Coffman says:

    Are you keeping it outside in the cold or did you bring it inside where its warm? I never know whether to leave outside or bring inside and let it do its thing. You lose all emerging data when you bring inside.

  4. For the most part, I keep all the insects I’m overwintering in a refrigerator that I keep just above freezing. I remove them after a few months, well aware that their emergence dates will be unnaturally early. I have several larvae that I found feeding on evergreen leaves after it got cold, and these I am keeping in an unheated shed, so they can continue to feed on warmer days if they’re so inclined. In the shed I also have some potted plants containing bark-mining larvae. This sedge miner is the one thing I have inside at the moment. At first, I figured it didn’t matter because it was so warm outside when I collected it. Now that it’s gotten cold again, I’m thinking my best chance at successfully rearing this larva will be to let it feed as much as possible before the leaf dries out.

    Emergence data are an important piece of an insect’s complete life cycle story, but I generally sacrifice this piece in favor of maximizing my chances of successful rearing, and getting as many of my overwintering bugs out of the way before my spring collecting starts. Emergence times can often be inferred from adult collection records

  5. Pingback: Spring is Coming! | BugTracks

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