Tuesday, April 26, 2011

Flatheaded Mayflies (family Heptageniidae): Live Photos

The most popular entry I've posted, in terms of the number of "page views," is my introductory overview of the family of "flatheaded mayflies" (1/8/11).   My goal this year -- and I think I've said this before -- is to get "good," live shots of every genus I find in every mayfly, caddisfly, and stonefly family.  Since I've now got pretty good photos of 5 of the 6 flatheaded genera we find in this part of Virginia, I thought I might bring them together all in one place so monitors can contrast and compare.  What these nymphs share in common is the "flat head" (!) and eyes that are completely dorsal (completely on top of the head).  Here we go.

1) Above: genus Maccaffertium (formerly Stenonema).  Nymphs in this genus can be very big: this one was close to an inch long, not counting the tails.  Photo taken on March 28 at Powells Creek.  This is the most common genus we find, and we find it all year long.  Genus TV: range by species, 0.3 -- 5.8.

2) Maccaffertium and Stenacron found together.  Note the "streamlined" shape of the Stenacron nymph.
Photo taken on March 18 at Whippoorwill Branch.  Stenacron is not a common genus in area streams.

3) Stenacron alone.  Photo taken same place and time as above.  Genus TV: range by species, 1.7 -- 7.1

4) Epeorus.  Note the fan-like, suction cup gills.  Not common in our streams, only found in the best, and normally seen only in winter.  Photo taken on February 20 at the Doyles River.  Genus TV: 1.2.

5) A second Epeorus -- this one mature and close to hatching.  Photo taken on March 24 at the Rapidan River.

6) Rhithrogena.  Gills are similar to those of Epeorus, but they form a complete oval on the ventral side of the nymph, and it has three tails instead of just two.   I think we start to see them in April, but I've only seen them in one stream to date.  This genus, too, prefers fast, clean water.  Photo taken on April 25 at Buck Mt. Creek.  Genus TV: 0.4.

7) Leucrocuta.  The nymphs in this genus are very, very small, and very, very fast on the rocks.  They are difficult to pick up without tearing off a leg or a tail.  I associate them with good water, good streams.  Photo taken on March 24 at an unnamed tributary to the Moormans.  Genus TV: 0.

8) Heptagenia.  I have not yet seen this genus this year.  I think it's a genus we only see in the summer and only in a few of our streams.  That's a thesis I may have to revise.  Until I find a live one to photograph, here's my preserved sample from last summer.  Genus TV: 2.8. 

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