Saturday, August 6, 2011
Acentrella nadineae: One of the Small Minnow Mayflies We Find in Our Streams in the Summer
In 2009 -- just two years ago -- W.P. McCafferty, R.D. Waltz, and J.M. Webb, published an article in the Proceedings of the Entomological Society of Washington entitled "Acentrella nadineae, A New Species of Small Minnow Mayflies (Ephemeroptera: Baetidae)" (issue 111 (1), pp. 12-17). An abstract of the article's contents can be found at http://www.bioone.org/doi/abs/10.4289/0013-8797-111.1.12.
They noted that this species had been found in southern and eastern Ohio as well as parts of North Carolina. I've now realized -- using a key to Ephemeroptera species -- that one of the small minnow mayflies that I've been finding all summer in a number of area streams is in fact Acentrella nadineae. I don't know if this is the first sighting of this species in the state of Virginia -- probably not -- but this might add to the data collected so far.
The nymph in the photo above was found in the Doyles River at Doylesville on June 23rd, and it nicely reveals two -- possibly three -- of the key features entomologists use in identifying this species: 1) the gills are large, asymmetrical, and have a line of "baso-medial" (running from the body to the middle part of the gill) grey pigmentation; 2) there are splotches of red or orange on the thorax and abdominal tergites; and 3) -- if you can see it -- the tarsi and tibiae of the first pair of legs when combined are not as long as the femora.
I have now found this Baetid species in five of our streams: Buck Mt. Creek, the Doyles River, the Lynch River, the Moormans River, and Powells Creek. These are all pretty good streams, and all of them are close to the Blue Ridge mountains. The tolerance value of this small minnow species is a mere 1.9, but I'm not surprised to find a low tolerance mayfly in these particular streams.
For the rest of this entry, I will simply post some of the photos I've taken of this species of Baetidae over the summer. Some of these nymphs are young; others are clearly mature. The photos reveal that, as with so many other mayflies and stoneflies, Acentrella nadineae nymphs get darker as they get close to hatching. Dates and locations are noted for each of the photos, and I've listed the photos in chronological order.
May 30th, Buck Mt. Creek. First sighting.
June 6th, Rapidan River (Madison County).
June 23rd, Doyles River (another photo of the nymph at the top of the page).
June 24th, Moormans River.
June 30th, Buck Mt. Creek -- young.
June 30th, Buck Mt. Creek -- mature (note the dark wing pads).
July 2nd, Lynch River -- young.
July 2nd, Lynch River -- mature.
August 2nd, Powells Creek.
August 5th, Buck Mt. Creek -- very young.
I will look at the "other" small minnow mayflies of summer that I've found in our streams in a subsequent entry. This one deserves an entry all of its own.