Tuesday, August 30, 2011

Montana Insects, Part III.: Baetidae (Small Minnow Mayflies)

I found very few stoneflies when picking up nymphs and larvae during my trip to Montana: 2 Perlids (common stoneflies), a few small Perlodids (only one that I could ID, and some small Giants.  But I did find a whole lot of mayflies: pronggilleds, flatheads, spiny crawlers (perhaps the dominant taxon of the insects I found), and a lot of small minnow mayflies.

I expected to have a lot to say about the identity of the small minnow mayflies that I collected -- as it turns out, I will say very little.  Having looked at all of my nymphs with the microscope, I can say that almost every one is genus Baetis, and almost every one, I think, is the same species -- but I don't want to guess what species that is.

Most Baetis nymphs have three tails; clearly visible hind wing pads; and labial palps that are rounded with a small "thumb".  Let's look at some pictures.

All of the nymphs in the pictures below keyed out as Baetis, exhibiting all of these features.

My reason for thinking these are all the same species is the fact that they seem to have two features in common: 1) a common abdominal pattern, and 2) the tails/cerci lack "medial banding" -- they are clear in color, darkening only at the tips (look again at the microscope photo above).

However, I clearly did find one Baetis nymph that was not the same species.   This I discovered with microscope study, and I could not find a "live" photo that matched it for sure.  In the photo below I've placed two nymphs side-by-side.  The one on the right (viewer's right) is the common pattern we see; the one on the left isn't the same -- it may be B. flavistriga.  And note that there is medial banding on the tails of this nymph.

In closing, I did find two nymphs that I don't think were Baetis.  They have only two tails and no visible hind wing pads.  Since I did not see any fore coxal gills, I'd guess they were Acentrella.  But I'll have to continue to work on identification.

Now back to the streams of Virginia!

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