Monday, August 29, 2011
Montana Insects, Part II.: More Species That I've Never Seen in Our Streams
1. And what do we have here? When I see "tusks" on a mayfly nymph I think of a "burrower": in this case I was sure I had found a Potamanthidae -- a "Hacklegill Mayfly." So I submitted this photo, along with some others, as "Potamanthidae" to Bugguide.net. Brady Richards moved the photos to Leptophlebiidae (Pronggilled mayfly), genus Paraleptophlebia! If you've been reading this blog, you know that Paraleptophlebia is the most common genus of Pronggilled mayfly we see in our streams in central Virginia. But -- we never see tusks. Apparently there are Pronggilled species out West that do have tusks -- and the nymph in the photo above clearly does have "pronged" (= forked) gills. Always new things to learn.
2. No problem here, it's a flatheaded mayfly (family: Heptageniidae). But what about genus? This one I figured out on my own: it's Nixe. This is a common nymph in the West that hatches -- following Knopp and Cormier (Mayflies, p. 150) -- (if this is Nixe simplicioides) from the end of July till the end of September. Note that morphologically, this genus is very close to Leucrocuta, the flathead we saw here a lot in the spring. Neither genus has fibrilliform behind the gill on segment 7. But Nixe nymphs have "intrasegmental setae" (fine hairs) on their tails -- Leucrocuta nymphs do not. Peckarsky (Freshwater Macroinvertebrates, p. 31) does list this as a genus that occurs in the East, but I've never seen one in our local streams.
3. In my last entry, I showed you pictures of three large, beautiful spiny crawler mayflies, all genus Drunella (they're the ones with the "tubercles" on the leading edges of the fore femora). Here's another Drunella, one that's oddly colored and oddly shaped. Using photos already posted on Bugguide.net, we can identify this as Drunella doddsii. I found this little fellow in Rock Creek, east of Missoula, on Monday, 8/22. I don't think this species occurs in the East.
4. Common netspinner (Hydropsychidae), genus Arctopsyche. Again, Peckarsky (Freshwater Macroinvertebrates, p. 101) lists this as a genus that occurs in the northeast: I've only seen it in my trips to Montana. It's fairly large, normally dark green, and is identified by examining the shape of the "gula". The gula is on the underside of the head and separates the two sides of the "chin" -- as it were, where they come together. On Arctopsyche nymphs the gula is clearly visible, and narrows from top to bottom, as we can see in the photo below.
5. Now, how about this one?
Obviously, given the gills on the underside of the tummy, another common netspinner. But I really wondered about the genus since I've never seen a netspinner with these colors before. Turned out to be Hydropsyche, one of the most common genera we see in this part of the state! Still, the colors are very special on this Montana version.
6. Not the best of photos, but one of the few Perlodid stoneflies I saw. This is genus Isogenoides. Peckarsky (Freshwater Macroinvertebrates, p. 71) lists it as a Perlodid we have in the East, and I know it's attested in Virginia. Still, to date, I've never seen this genus outside of Montana. This is a genus that is keyed out in two ways. 1) It has submental gills.
And 2) "[The] median ridge of [the] mesosternum extends anteriorly beyond [the] fork of [the] Y to [the] transverse ridge." (Peckarsky, p. 71) Photo please.
Below -- setting off for a day of fishing on the Blackfoot River, north of Missoula, MT.