Friday, May 9, 2014

Genus Leucrocuta flatheaded mayflies: an update on species ID

Since I'm starting to find mature Leucrocutas, I thought I might comment again on the problem of species ID.  Steven Beaty ("The Ephemeroptera of North Carolina," p. 19) lists 5 Leucrocutas for North Carolina: aphrodite, hebe, juno, maculipennis, and thetis, but he urges readers to leave identification at the level of genus since the nymphs have not yet been fully described at the level of species.

Having found the nymph in the photo at the top of the page on May 4th, I contacted Beaty (e-mail) to see if work has been done on this issue.  The answer is "yes," but he does not know when that work will be finished and published.  He added that the nymph I had found "might" be L. thetis -- but that ID would be based on a key that is, according to Beaty, "woefully out-of-date."  The book in question: A.R. Brigham, W.U. Brigham, and A. Gnilka, eds., Aquatic Insects and Oligochaetes of North and South Carolina, 1982.   (You can find used copies for around $400.00.)

I think I've found 4 different Leucrocutas to date in our streams.  I'll discuss them by number.


While Beaty is hesitant to do any species ID for Leucrocutas, I have two sources that ID this nymph as L. hebe.  The first is an L. hebe photo published by Donald Chandler on the Discover Life website:  The second is the study of mayflies by Knopp and Cormier, Mayflies: An Angler's Study of Trout Water Ephemeroptera.  On p. 152, they describe L. hebe as "grayish brown with paler U-shaped spotting on body."  Those spots are easy to see.


When this nymph is ID'd, the pale spots on terga 1, 7-8, and possibly 9 will probably be used in the description.

Knopp and Cormier (p. 152) describe L. juno as a nymph with "tergites 1, 7, 8, 9 white."  That could be true of the nymph in our picture when it matures.  Clearly, this is a small one, and the colors/patterns are not yet fully developed.  However, this nymph looks nothing at all like the L. juno nymph in a photo by Chandler. (

Chandler's L. juno looks more like our nymph #3.

This Leucrocuta is one that I've only seen in the small headwater streams in Sugar Hollow.  The femora on this type of nymph are very distinctive: note the two pale dots, one in the middle and one at the tibial joint.  Another feature that might be distinctive -- the paired pale spots on most/all of the terga.


And number 4 would be the latest species I found, the one that might be L. thetis.  There seem to be 5 pale spots on the femora of this type of nymph, and possibly medial pale spots on some of the terga.  Perhaps those will be used in a key to this species.


There is another species that we surely ought to be seeing: L. aphrodite.  Beaty notes that "Most Leucrocuta in the Piedmont are probably aphrodite," but he has tells me that the aphrodite nymph has not been described, just the adult.  Knopp and Cormier do describe -- and illustrate -- L. aphrodite: "tergites 9-10 pale."  I haven't seen anything like that, and I don't know on what their description is based.

So that's where we stand, and I doubt that we'll go any further until the entomologists can figure this out.

Other photos, nymphs 1-4.


(Quick ID for genus Leucrocuta -- 1) it's the "fat-headed flathead" -- head wider than pronotum; 2) no fibriliform posterior to gill 7.)

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