New Insects from Oregon: Drunella spinifera and Rickera sorpta

It's been awhile since I've posted an entry, but it's been awhile since I found anything new.  But I lucked out last week when we went to visit our daughter in Oregon.  On a trip up to Mt. Hood, we stopped at a small stream in which I found some new -- for me -- insects.

Let's start with the easy one, the spiny crawler mayfly, Drunella spinifera.  (In the photo above and the photo below)

As I always do when I try to ID bugs from the Northwest, I turned to the website managed by Roger Rohrbeck, PNW Mayflies (Fly Fishing Entomology).  Rohrbeck describes seven different species of Drunella nymphs, and the one that works for us is Drunella spinifera.   His description reads: "Femora of front legs very broad, but don't have bumps on front edge; long sharp tubercles on back of head; abdominal tubercles 8-9 more than twice as long as 2-7."  Here's a look at the fore femora:

Other species of Drunella do have bumps on the front edge.  E.g., in case you've forgotten, here's a look at the fore femora of Drunella cornutella, a species we find in our streams in VA.

Dramatically different.  The shot I took of the tubercles on the head --

don't show the "sharpness" very well (bad angle on my part), but check out the tubercles on the abdominal segments.

The tubercles on segments 8 and 9 differ markedly from those on 2-7.  No doubt about it, our nymph is Drunella spinifera.  I might add that on his website "troutnut.com," Jason Neuswanger notes that this is a species that "prefers cold water," and inhabits "high elevation headwaters."  We were at about 3000' ASL.
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Now on to the toughy.

As you can see,  it was a very small stonefly nymph which makes the ID all the more difficult.  However, I have reason to believe that it was Rickera sorpta.  This genus and species is described on p. 440 of Stewart & Stark, Nymphs of North American Stonefly Genera.  There, the head is described in the following way: "Head with dark, broad, irregular U-shaped mark connecting ocelli; light oval interocellar spot. Light area anterior to median ocellus."

On target so far.  On the lacinia -- "Lacinia triangular and unidentate, with 5-6 basal marginal spinules and 2-3 medially located marginal spinules."

Unidentate for sure.  I didn't note any spinules, but this was a very small, very young nymph.  Now for a critical feature.  "Y-arms of mesosternum meet posterior corners of furcal pits, and transverse suture connects anterior corners of furcal pits."  The connecting suture is illustrated on p. 442 (Fig. 14.50), and it appears to be in the shape of a slight arc.  Here's the best photo that I could manage.

I've put a rectangular box around this suture to help us focus.  I'd say they're connected for sure.  One other feature.  Rohrbeck adds that there are "dark and light stripes on the abdomen" (PNW Stoneflies). 

And there they are. 

I only hesitate on my ID because there is another taxon -- Kogotus nonus -- that looks a lot light our little nymph.  The head pattern's much the same, and there are dark and light stripes on the abdomen, and the lacinia is unidentate.  This is one that I found a few years ago in Montana.

How do they differ?  It has to do with the presence or absence of that suture connecting the furcal pits of the mesosternal Y-ridge.  It's present on Rickera, absent on Kogotus.  I'll stick with my ID of Rickera sorpta, for the moment at least, since I do see that suture on our small nymph.

So much fun to find something new and to work on the species ID.  I should note, by the way, that I'm now posting photos on Instagram.  Look for me under "buddhabob2hanlubo". 

Cinygmula subaequalis: do the nymphs differ by gender?

One of the flatheaded mayfly nymphs that easy to ID, even just using a loupe in the field, is Cinygmula subaequalis (subaequalis is the only species in the Southeast).   We need only note the two bumps at the sides of the head, which are the maxillary palpi.

But the color patterns I've seen on the nymphs that I've found aren't always the same.  Some, like the one in the photo at the top of the page, are essentially brown, others like this one

have a distinct pale area on the frons (the forehead). 

Last Sunday, I found two nymphs at the Rapidan River, one of each type.

It occurred to me that this might be a gender distinction, something we commonly see with small minnow mayflies, so I ran this by Steve Beaty.  He wasn't convinced, feeling that those with the pale areas on the top of the head might simply be nymphs that have just recently molted.  But I still wonder about this for one very good reason: the distinction is one that's consistent.  That is to say, where there are pale areas on one of the nymphs in the photos above, there are pale areas on the other nymph as well.  Have a look.

There's the spot on the head -- which is shaped the same on both of our nymphs, a second spot on the mesonotum, and the first tergite is pale.  (So too are terga 9 and 10, but that is also true of our solid colored nymphs.)  This is something I wouldn't expect if this were simply a matter of molting.

Time will tell, but I'll keep an eye out for these features on other nymphs that I find.
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Some other nice pics at the Rapidan River last week.

1) A fairly mature Ephemerella subvaria.

2) The stonefly, Agnetina capitata.

And 3), a rather spectacular pronggilled mayfly, Neoleptophlebia assimilis.

If you're a fly fisherman, pretty clear that the Blue Quills are hatching.

An odd pair of spiny crawlers at the Doyles River yesterday

It's the time of year when we see a lot of spiny crawlers in all of our streams, for the most part, genus Ephemerella.  E. invaria nymphs are present in appreciable numbers from February to April; E. dorothea nymphs show up in HUGE numbers from April to May to June.  I saw a lot of them yesterday at the Doyles River including this striking pair, male and female.

It wasn't until I got home and downloaded my photos that I noticed just how striking they were.  What's unusual is the orange spots on the sides of terga 5 and 6 and at the top edge of the mesonota.

Thinking I might have found a species I'd not seen before, I did the microscope work, using Beaty's "The Ephemeroptera of North Carolina" as my guide.  In the end, they keyed out to E. invaria, or rather, "E. invaria group".  Let me review the critical features.

Nymphs 6-13 mm; pale transverse stripe between eyes, may be interrupted medially; tarsal claws with 5-10 denticles; abdominal terga with short, sharp, paired submedian tubercles on segments 2-9, rarely on 2, sometimes barely discernible on segments 3 and 8, small on 4-7, rarely on 9; posterolateral projections on abdominal segments 3 or 4-9 (variable to absent on 3); may have dot-dash pattern on pale ventral surface and speckling on last few segments.  ("The Ephemeroptera of North Carolina," p. 52)

1) Our male nymph measured 6 mm, the female -- the larger and lighter of the two -- measured 8.

2) The pale stripe between the eyes is clearly visible on both of our nymphs; they don't seem to be "medially interrupted."

3) I could see 5 denticles on the tarsal claws, with a dark spot behind them (more denticles?).

4) On the female nymph (didn't check the male), there are paired, sharp pointed tubercles on segments 3-9.  In this photo, I've pointed out those on segments 4 and 5.  (Note, the "tubercle" is just that part of the pale spot that projects beyond the rear edge of the terga.)

5) There are posterolateral projections on terga 4-9, and yes, the last few ventral segments are speckled, and the dot-dash ventral pattern shows up very clearly.

So, Ephemerella invaria nymphs for sure.  But two things to keep in mind.  Beaty notes that "This is the most variable Ephemerella species in terms of size, color pattern, and size of tubercles," number one, and two, E. invaria is now considered to be a "group," which includes the species E. inconstans and E. rotunda.  No way to know which member of the "group" I found without finding some adults.
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The other taxa that is crowding our streams at the moment is Isoperla montana, the nymphs that hatch as "Yellow Sallies" for you fly fishermen.  They were also prominent yesterday.

The small winter stoneflies are filling our streams

It's the kind of day -- cold and overcast -- when I normally forego taking photos, but I changed my mind when I collected this little nymph.  A fully mature small winter stonefly, Allocapnia pygmaea, female.  The leafpacks are full of these nymphs at the moment.  Not my best photos, but nice enough to share.

Acroneuria colors: I still get surprised.

I came upon this photo the other day when reviewing my files and immediately concluded it was the common stonefly, Acroneuria abnormis.  The reason is simple.  A. abnormis nymphs, in my mind, are always this color of brown.   For example...

True, as with the nymph in this photo, they often have terga that are banded, but still the basic color is brown.  And, you may recall, on some nymphs the terga are totally brown.

Closely related to A. abnormis is A. carolinensis.  Both species have a light "M" pattern on the head, lack a row of setae at the back of the head, and A. carolinensis nymphs also have banded terga.

But A. carolinensis nymphs, as you can see are basically yellow or orange.

So it appears to be easy to tell them apart by seeing the color.   The nymph at the very top of the page is basically brown, so it must be A. abnormis -- right?  Wrong, and I should have known better.  It is morphology that we have to use in determining species; pigment is an unreliable character.  And "morphologically," abnormis and carolinensis nymphs differ in one important respect -- the banding shades are reversed.  On A. abnormis nymphs, the dark band is in front, the light band at the back, on A. carolinensis, it's just the opposite. 

Back to our nymph at the top of the page.

Yes, it's basically brown, but look at the terga.  This nymph is A. carolinesis.  And, we can find the same with A. abnormis.

Basically yellow, but the lighter bands on the terga are at the back.  It's A. abnormis.

Just a reminder, don't be too quick to jump to conclusions, and I've been guilty of this.  True, the color's a good indication, but the tergal banding is the key thing to use.

Some photos from my files

I've started posting pics on Instagram ("buddhabob2hanlubo"), so I've been looking through my files to find things that are post-worthy.  To my surprise, I've found a lot of nice pics that I'm not sure I've ever used in this blog.  So, here's a look at some of my favorites.

1) Above, a pair of small winter stoneflies -- Allocapnia pygmaea -- female on the right, male on the left.

2) A second small winter stonefly, female, one that was close to hatching.

3) Some small minnow mayflies.  This one is Baetis pluto.

4) Small minnow mayfly, Baetis tricaudatus.

5) Small minnow mayfly, Acentrella turbida.

6) And small minnow mayfly, Heterocloeon curiosum.

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7) Spiny crawler mayfly, Ephemerella dorothea.

8) Spiny crawler mayfly, Ephemerella dorothea.

9) Spiny crawler mayfly, Ephemerella subvaria.

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10) And some caddisfly larvae.  Here, some common netspinners, Diplectrona modesta.

11) Lepidostomatidae, genus Lepidostoma.

12) Weighted casemaker, Goera fuscula.

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Fun.  Something to do while we wait for warmer temps -- and it would be nice if those temps come with some rain!