Saturday, April 14, 2018

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.
________________

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.

Saturday, April 7, 2018

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 EphemerellaE. 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.
________________

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.



Tuesday, February 6, 2018

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.




Monday, February 5, 2018

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.

Tuesday, January 2, 2018

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.

_________________

7) Spiny crawler mayfly, Ephemerella dorothea.


8) Spiny crawler mayfly, Ephemerella dorothea.


9) Spiny crawler mayfly, Ephemerella subvaria.

__________________

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


11) Lepidostomatidae, genus Lepidostoma.


12) Weighted casemaker, Goera fuscula.

_______________________

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

Thursday, December 21, 2017

A few photos from Entry Run


I drove up to Entry Run in Greene County on Tuesday.  Didn't see anything out of the ordinary, but I got some nice photos worth posting.

Above and below, brushlegged mayfly, Isonychia sp. (probably bicolor).


I still hope to find a nymph with single forecoxal gills -- not sure it's going to happen.  All of the Isonychiidae I've found so far have a "cluster of filaments" at the forecoxae, meaning I can't ID them to the level of species.  On this nymph, those gills show up in this live photo, no need to go to the microscope.

_________________

I wasn't at all surprised to see some of our winter casemakers, a Lepidostomatidae,


and a Thremmatidae (formerly Uenoidae), Neophylax consimilis.

__________________

And, to my surprise, I also found a spiny crawler, Ephemerella subvaria, the nymph of "many colors."



There was one odd thing about this one: the pointed tubercles on terga 5, 6, and 7 were pale colored.


I'm pretty sure that on the nymphs that I've found previously, those tubercles were all black.  Strange.  I plan to look into this.  Probably just a local variation.