Saturday, April 15, 2017

Isoperla davisi at Buck Mt. Creek

A species of Isoperla that I haven't seen for four years -- Isoperla davisi -- one that I've only seen at Buck Mt. Creek.   Better review how we arrive at the species ID.

We rely on the patterns we see on the abdomen and the head.  "pre-emergent nymphs 7.0-8.0 [mm].  Lacinia recedes from base with 6-8 stout marginal spines below subapical tooth; both pale area anterior to median ocellus and pale ocellar spot enclosed; transverse brown bar on anterior frontoclypeus wider than brown area that encloses the anterior pale median area." (Steve Beaty, "The Plecoptera of North Carolina," p. 59)

Our nymph is 8 mm long.  The lacinia is as described,

as is the head pattern.

Beaty continues: "dorsum of abdomen with distinctive longitudinal '5-lined' banding; median and sublateral bands darker and usually narrower than submedial bands and with intervening pale narrow lines."  

If you go to NatureServe Explorer ( and enter "Isoperla davisi," you'll see that the common name for this species is "Alabama stripetail."  Curiously, they fail to note that this species is found in both Virginia and North Carolina (here only listed for Alabama, Florida, and South Carolina.)

Good to see this one again.


It was a great day at Buck Mt. Creek.  Lots of insects around, including a bunch of Nemourids, the genus we see in the Spring -- Amphinemura.  (Amphinemura delosa.)

These are the Nemourids with the "cervical gills," which makes them very distinctive.


I saw a lot of Amphinemura, but without any question, the bug of the day in terms of sheer numbers was the small minnow mayfly, Plauditus dubius.   I saw both male and female, and almost every nymph that I saw had black wing pads = ready to hatch.

They can be distinguished by gender with a quick look at the eyes -- big eyes on the males (first photo) -- but the abdominal patterns differ as well.  While the pattern is hard to see on our male since it's so black, we can see the key feature on the female.  "female -- median spots on terga 2 and 6."  (Beaty, "The Ephemeroptera of North Carolina," p. 22)

The dark median band on the tails is present on both male and female.

The weather's been great so I hope to get out a lot more.   The warm temps and low water we've had most of the year, mean that things are ahead of where we expect them to be.  To wit, I'm already finding Isoperla holochlora nymphs.  Very early.

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