Saturday, January 28, 2012

Malirekus hastatus in Our Own Backyard

So, last week I drove up to the Rapidan River in Madison county and found -- for the very first time -- the Perlodid stonefly, Malirekus hastatus, and today I found two of them in one of the tribs I study in Sugar Hollow.  No need to go far from home to find quality insects -- just head for the Blue Ridge Mountains.

Some more photos:


Since I posted the 1/21 entry on Malirekus hastatus, I've learned two things about this Perlodid.  1) Malirekus hastatus nymphs and Malirekus iroquois nymphs look exactly the same, but M. hastatus has submental gills; M. iroquois does not.  M. hastatus is found in the southeast; M. iroquois in New England and the mid-atlantic.  So, I guess we now know for sure that central Virginia's in the south!  Joking aside, the precise dividing line between the two species is not known for sure, so maybe we've discovered something important.  2) The second thing I've learned about M. hastatus nymphs is that they're very aggressive!  I collected a number of flatheaded mayflies this morning, Epeorus pleuralis, and made the mistake of putting them in the same bowl with my Perlodids.  When I next looked, both of my M. hastatus nymphs had Epeorus nymphs in their mouths!  And, when I was taking my photos, the M. hastatus nymph was constantly chasing an I. similis nymph around the side of the dish.  Happy to say, the I. similis always escaped.

Close call!

Important diagnostic features for M. hastatus, again, are the pale dots on the head that are anterolateral to the rear ocelli, the pale area that forms the ocellar triangle, and the "conical-shaped," tiny, submental gills.

Other nice findings today --

1. Lots of Isoperla similis nymphs -- much smaller in size that M. hastatus.  And note the different head pattern: no pale area in the ocellar triangle, and there are pale "spaces" that are anterolateral to the ocelli, but they're not in the shape of ovals.

2. A real surprise -- a Gomphid (Clubtailed dragonfly), genus Ophiogomphus, with wing pads that make it look fairly mature!  It was 14mm long -- close to 3/4 of an inch.

3. And another surprise, I found three Limnephilid caddisfly larvae, genus Pycnopsyche, all three in the three-sided cases made out of pieces of leaves.  One was kind enough to venture out of its home.

4. And finally, a photo of one of the many flatheaded mayflies I found -- all Epeorus pleuralis (Quill Gordons to you flyfishermen).  Look for them on the bottoms of rocks.   On one large rock that I turned over, there must have been 15-20 nymphs that scurried for cover.

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