A "Cheat Sheet" for "Common stonefly" genera (Perlidae)

To my surprise, my "Cheat sheet" for flatheaded mayflies was quite a hit, so let me see if this is of interest as well.  Volunteers come to quickly ID common stoneflies (family Perlidae) by the branched gills that stick out to the sides behind each of the legs.  But I think they could also ID the Perlidae to the level of genus with just a smidgeon of work -- and the use of a loupe.  Again, I hope this adds to your enjoyment of picking bugs off of the nets.   Just repeat this mantra -- "heads and tails" -- that's all you need to look at to determine the genus ID.  Look at the top of the head and the base of the tails, specifically, as we'll see, you have to ask are "anal gills" present or absent?

               A Cheat Sheet for "Common stoneflies" (Perlidae)

 1.  only two ocelli on head: Neoperla

2. closely set row of spinules on the back of the head, regular and complete

a.  anal gills present:  Agnetina

b. anal gills absent: Paragnetina

3. spinule row at back of head irregular, can be sinuate with gaps – Perlesta

4. no row of spinules at the back of the head

a. pale "M" pattern on head, anal gills present or absent: Acroneuria

b. no "M" pattern on head, but large pale area in front of anterior ocellus, anal gills present: Eccoptura

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So here we go.

 1.  only two ocelli on head: Neoperla

Ocelli are "simple eyes" -- they look like black dots-- on top of the head, two lateral and one anterior.  Together they form the "ocellar triangle."  On Neoperla nymphs, the anterior ocellus is missing: on all other genera it's present.  As below.

Neoperla is a genus I've only seen in two of our local streams, and it's only around in the summer.

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2. closely set row of spinules on the back of the head, regular and complete

a. anal gills present:  Agnetina

b. anal gills absent: Paragnetina

Here's what they look like.

This Paragnetina (P. fumosa), by the way, was in Buck Mt. Creek for local readers.  The other species I see is P. immarginata -- this one --

which I've only seen at the Rapidan River.

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3. spinule row at back of head irregular, can be sinuate with gaps – Perlesta

Perlesta nymphs have anal gills, but that irregular row of spinules really nails it down.  I've seen two different types: one that's densely "freckled,"

and one that's not.

Look for Perlesta nymphs in our streams in May and June -- some in April -- they're not to be found the rest of the year.

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4. no row of spinules at the back of the head

a. pale "M" pattern on head, anal gills present or absent: Acroneuria

b. no "M" pattern on head, but large pale area in front of anterior ocellus, anal gills present: Eccoptura

Acroneuria -- more than one color

Eccoptura

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Don't rely solely on color: always use morphological features: anal gills present, anal gills absent?  row of spinules present or absent?  If present, what type of row do you see?  If there's no row of spinules, is there an "M" pattern, or a large pale area at the front of the head?

And what are you most likely to see?  No question about it -- the chocolate brown Acroneuria with light bands on the posterior edges of the abdominal terga, which is Acroneuria abnormis.  It's the most common "common stonefly" we see, and it's in our streams -- various sizes -- 12 months of the year.

Give it a try.  Have fun!  Just remember the mantra -- "heads and tails."
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(I have time to play around with this kind of thing because our streams are virtually dry.  We need rain, really, really badly, and lots of it.)