Friday, June 13, 2014

Back to the ID of those pesky Maccaffertium flatheads from Buck Mt. Creek and the Doyles

Back from Europe -- and back to streams that are high and off color.  Ugh!  Still, I also came back to some help from Steven Beaty with the species ID of the Maccaffertium flatheaded mayflies that I found at Buck Mt. Creek on 5/15 -- in the picture above -- and at the upper Doyles River on 5/24.  (I had sent him the nymphs in a vial.)

On this nymph from Buck Mt. Creek -- with the pronounced banding on the femora -- according to Beaty, it is probably M. modestum.  This was determined by slide mounting the mouth parts and the tarsal claws and noting the ventral pattern.  That means there are "more than 30 hairs and 2-3 spine-like setae on [the] maxillary crown," and that the protarsal claws lack denticles." ("The Ephemeroptera of North Carolina," vers. 2, p. 35)

While I can visually ID M. vicarium, M. merririvulanum, and M. pudicum by noting their dorsal and ventral patterns, M. modestum cannot be ID'd in that way ("highly variable dorsal and ventral patterns," Beaty, p. 35).  Beaty notes "two common ventral patterns" for M. modestum, but our nymph has no pattern at all.

What we can see in this view of the venter is that on M. modestum nymphs "posterolateral projections [are] absent anterior to segment 6" (p. 35).

By the way, Donald Chandler has posted photos of M. modestum on Discover Life, and his nymph looks a whole lot like mine.  (See:

And what about this nymph that I found in the Doyles River on 5/25?

My initial conclusion was right: it's M. ithaca, a species we commonly see at this time of year (the "Light Cahill" for you fly fishermen).   Again, Beaty mounted the mouth parts and the protarsal claws and took a close look at the venter.   On M. ithaca nymphs there are "15-35 (usually 20-30) hairs and 4-6 spine-like setae on [the] maxillary crown."  ("The Ephemeroptera of North Carolina," p. 34)  I could see 5 spine-like setae on the crown with my microscope; I was not able to count the hairs.  I could also see with my microscope a denticle (tooth) on the protarsal claws.

Beaty says that M. ithaca claws usually lack denticles (p. 34), but in an email he sent me two years ago, he noted that they may or may not have denticles.  Clearly, our nymph had them.

As I had noted on 5/24, the ventral pattern we find on our nymph closely resembles that of M. mediopunctatum -- but it's not exactly the same.  Here's what we have on our nymph:

 While M. ithaca and M. mediopunctatum both have an inverted "U" on segment 9, the "sternal maculations" on segments 3-8 (the cross bars) are curved on M. ithaca; they're fairly straight across on M. mediopunctatum, and they're flush with the anterior edges of the segments.  (See:

So there you go.  Nothing "exotic" or new.  But once again we see the need for close-up microscope work to be sure of species ID.

And less than one week ago I was enjoying my lunch in Amsterdam by this lovely canal!

No comments:

Post a Comment