Ventral Patterns and the Identification of Flatheaded Mayflies to the Level of Species

A short time ago -- on June 22nd -- I posted an entry on fly fishing and the major species of flatheaded mayflies.  Last night while surfing the web I discovered a web page that is extremely useful for those of us who wish to pursue this information.   The page in question has photos by Donald S. Chandler of a number of key flatheaded species, showing that the "ventral pattern" is crucial in species determination.
The website is "Discover Life," and the page in question is: http://www.discoverlife.org/mp/20q?search=Maccaffertium.

This morning, in viewing the "tummies" of the Maccaffertium nymphs in my reference collection, I discovered what appear to be five different patterns: I have no doubt what at least two of them are.  Chandler ID's the pattern above as that found on Maccaffertium vicarium nymphs -- for fly fisherrmen, the "March Brown" hatch that we anticipate every spring.   I think this was a nymph that I found on March 28th in Powells Creek in Crozet -- the one in the photo below.

This is a big nymph, and the "March Brown" is a big terrestrial mayfly.  Knopp and Cormier (Mayflies: An Angler's Study of Trout Water Ephemeroptera, p. 176) give a hatch range for M. vicarium of mid-May through mid-July here in the East (but the hatch might start even earlier in the southeast).

The other pattern I can ID for sure is this one:

This is Maccaffertium ithaca -- the "Light Cahill" for fly fishermen -- and this is one of the flatheads I found yesterday at the Lynch River.  Here's another look at that nymph.

This is an insect that hatches throughout the summer, normally from late afternoon until dark.  Knopp and Cormier (p. 176) give a hatch range for M. ithaca of mid-June through mid-August.  So, no surprise that the wing pads on this nymph are already quite long.

The patterns I found that I can't really ID for sure -- nor can I match them up now with any flatheaded photos I have that I can date.  Nonetheless, here they are.

1)  (This may be M. modestum which hatches from the beginning of June through the end of July.  Feel free to check this against the photo at the website noted above and let me know what you think.)

I should add that, if you click on the photo and look at the much larger image, you'll see that there are "posterolateral spines" (sharp pointed endings) on abdominal segments 7-9 (on this point, see p. 177 in Knopp and Cormier).  That feature is characteristic of M. ithaca, M. modestum, and M. pulchellum.  M. modestum and M. pulchellum hatch as the "Cream Cahill".  These hatch from the beginning of June through mid-October.

2) another pattern (also could be M. modestum)

3) and one more (is this a variant pattern for M. ithaca?)

4) Oops!  Sorry.  I do have another.  (Is this a young M. ithaca?)

I'll be checking out "bellies" on flatheaded nymphs from now on -- and matching them with the dorsal view of the insect.  I wish now that I had kept the other good sized nymph that I found yesterday.  But, alas, the one that got away!  There's just no end to the neat things that we can learn.