Thursday, June 14, 2012

Maccaffertium ithaca: the Flatheaded Mayfly from the Lynch River Last Week

I was able to identify this flatheaded mayfly I found on 6/7 at the Lynch River -- with some help from Steven Beaty, and from his description of the various Maccaffertium species in his "The Ephemeroptera of North Carolina," p. 19.  It's an M. ithaca nymph, a popular mayfly -- the adult anyway -- with fly fishermen since it produces an important hatch on summer evenings -- the "Light Cahill" hatch.   Knopp and Cormier (Mayflies, p. 176) give the hatch dates for the Light Cahills here in the East as mid-June through mid-August.  This nymph has very long wing pads, and I saw another nymph on 6/7 on which the wing pads were already black.

Beaty describes M. ithaca in the following way:

"M. ithaca -- nymphs 9-14 mm; 15-35 (usually 20-30) hairs, 4-6 spine-like setae on maxillary crown; sterna 5, 6, or 7-8 with transverse sternal bands with anterolateral extensions, sometimes reduced to spots;  usually no denticles on tarsal claws.  Primarily a mountain taxon."  The tolerance value for M. ithaca is 3.0.

The nymph in the photo above was 11 mm, and I counted 20-30 hairs on the maxillary crown and what looked like 4-5 spines.  Of the transverse bands on the sternites -- I was able to get a picture.  On this nymph we can see the "anterolateral extensions" on sternites 7 and 8.

M. ithaca nymphs resemble M. modestum nymphs.  But, there are always denticles (teeth) on the tarsal claws of M. modestum; there were no denticles on these tarsal claw.

I'm pretty sure that I saw these nymphs in the Lynch river last year at this time as well.  At the time, I thought they were M. ithaca nymphs, and now we know it for sure.

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