Saturday, April 28, 2012

A "hat-trick" on Flatheaded Mayflies at the Doyles: E. pleuralis, E. vitreus, and Rhithrogena

And all three species in the same set of riffles!  Number 1: genus Rhithrogena -- three tails and fan-like gills that form a complete oval on the ventral side of the abdomen.

Number 2: Epeorus pleuralis -- two tails with fan-like gills that do not connect on the ventral side of the abdomen; tracheation in the gills is barely visible.

And number 3: Epeorus vitreus -- two tails with large, fan-like gills in which the tracheation is very pronounced.

The rocks were covered with flatheads: most numerous  -- the Rhithrogenas.  This was one of the few places I've visited in recent weeks where spiny crawlers were outnumbered by some other insect.  Another view of the three.

Tolerance values: Rhithrogena -- 0.0; E. pleuralis -- 1.5; E. vitreus -- 1.2.  Pretty good water in the Doyles River at Doylesville.

I was surprised to see all three flatheaded species together.  But there were other surprises in store.  Like this common stonefly.

This one is genus Perlesta, and if you look back to blog entries for last June and July, it will be clear that  we normally see Perlestas in early summer -- not in late April, at least not any that are already looking fairly mature (note the shape of the wing pads)!  The features we use to ID this species are the wavy, incomplete row of spinules on the occipital ridge and the branched subanal gills.

The other "surprise" was something I've not seen before: a fully mature Nemourid stonefly, genus Amphinemura, one with black wing pads.  Sorry for the poor definition -- this is a very small insect (around 5 mm).

Pretty cool.

Of course, there were spiny crawlers, and they were E. dorothea.  Orange and brown seem to be common colors.

Below: an I. holochlora Perlodid stonefly sees its reflection in the petri dish.

Oh.  And I was hoping to find some small minnow mayflies -- and I did, but by then it was too overcast to get a good photo:  Baetis intercalaris.

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