Saturday, December 15, 2012
Fly Fishermen: Get Out Those Midge Imitations!
Christmas is coming -- the midges are already fat! Yes, it's that happy season that fly fishermen either love or dread, when we turn to those fly boxes with the size 18-22 hooks -- the midge imitations, larvae and adults. But as we get older -- I speak from experience -- it's not very easy to thread tippet through the eye of those tiny hooks!
While I'm finding a lot of stonefly nymphs in those leaf packs and on the bottoms of rocks, I'm also starting to see a fair number of midges -- they're getting big now. This is one that I photographed on Thursday up at South River, but I've been seeing them in just about all of the streams I've explored in the last couple of weeks. While I didn't measure this larva, I'd guess that it was close to 10 mm.
While there are several families of midges, the midges that we commonly see are "Chironomids," and anyone who monitors streams knows that "The midges (order Diptera, family Chironomidae...) account for most of the macroinvertebrates in freshwater environments." (Robert W. Bode, p. 225 in Barbara Peckarsky, et.al., Freshwater Macroinvertebrates of Northeastern North America.) And we also know, as Bode goes on to say, that "in many aquatic habitats this group constitutes more than half of the total number of macroinvertebrates species present." Stream samples in spring, summer, and fall, are often dominated by midges, especially samples taken in marginal water.
Can amateurs identify midges to the level of genus or species? No. Forget it. The Peckarsky key lists a total of 151 genera in six subfamilies, and Merritt, Cummins and Berg (p. 847) say that in North America alone there are at least 1200 species -- there may be as many as 2000. And Bode points out that "Almost all identifications of chironomid larvae require that the specimens be slide-mounted and examined through a compound microscope." (Freshwater Macroinvertebrates, p. 227) So, they will be "midges" or "Chironomids" in the entries I write.
Stream monitors rarely see what they actually look like. On a sample net, all they see is a tiny, clear to yellow filament that wiggles around like a snake when you squirt it with water. But with a microscope -- or a good macro lens -- we can easily see the head and the eyes and the little "prolegs" (unjointed), one pair in front and one pair in the rear. We can make them out in this photo taken on Thursday,
but they show up even better in this photo I took in March of last year.
One more thing in what will surely be the only entry I'll be writing this season with a focus on midges -- a lot of fly fishermen use red thread to tie their larval imitations. There are red midges -- but I've seen very few. Ninety-nine percent of the midges you're going to see are -- like those in the photos above -- clear to yellow: I also see green ones fairly often. Red midges are "red" from the hemoglobin in their bodies. That means they need less dissolved oxygen from the water to live, so you're likely to see them only in water that's severely degraded. That's not where you'll be finding the trout!
Another member of the order Diptera (True Flies) that I commonly see at this time of year in the leaf packs is the Crane Fly -- family Tipulidae. And on rare occasions I find the genus I found in the South River on Thursday.
The genus is Hexatoma, one that is "found in sand or gravel near margins of clear, cool brooks and streams." (Peckarsky, Freshwater Macroinvertebrates, p. 201) This is a genus I've only seen at the South River, the Rapidan River, and in some small streams in Sugar Hollow. Most stream monitors never see this one. The genus we commonly see -- and I see a lot of them at this time of year -- is Tipula, and it's a larva that monitors can spot right away.
Most are grayer than this one, and when the body's constricted (this larva's stretched out) they look pretty chubby. Actually, they're sort of gross, but the adults can be beautiful things. Two features stand out on Tipula larvae -- the "welts" that form between the abdominal segments, and the "spiracular plate" at the rear end. Now look at our Hexatoma.
No welts; no spiracular plate. At the posterior end of Hexatoma larvae we find four lobes with setae at their tips. We can see some of those lobes on this larva I found in November, 2011.
But what's really distinctive on the larvae of Hexatoma is the seventh abdominal segment. It often forms into a bulb: I've never seen this on a live larva, but it's easy to see on a larva that's been preserved.
Next week -- back to stoneflies and mayflies and caddis, I hope. But, we're being hampered by low water conditions. A drought watch has been issued for our part of Virginia. We need rain, but there's nothing in sight.