Saturday, March 16, 2013

The Spiny Crawlers of Spring: Ephemerella dorothea

The spiny crawlers I've seen in our streams starting in late December (12/21, Doyles River) have all been E. invaria in terms of the species (see the entry posted on 1/13/13).  But I've noted a number of times that E. invaria is not the spiny species that shows up in huge numbers in a lot of our streams in the spring: that's E. dorothea.  Well, E. dorothea is here (the PED -- "Pale Evening Dun" for fly fishermen).  I found this one yesterday in the Whippoorwill Branch of the Mechums.  In fact I found a lot of E. dorotheas yesterday in this tiny stream, most of them still pretty small.   Some were in leaf packs, others were crawling around in patches of moss on the rocks -- always a good place to look for nymphs of this species.

The nymph in the photo above is a bit atypical for the species.   It measured 9.5 mm: the usual range for the species is 6-8 mm according to Beaty ("The Ephemeroptera of North Carolina," p. 27).
Many of the nymphs that I saw yesterday fell into that range: this one was 7.5 mm.

Since we're moving into the season for E. dorothea, it might be worthwhile to review the features we use for species ID.  Wherever I can, I'll use close up photos from that large nymph at the top of the page.  In Beaty we read:

E. dorothea -- nymphs 6-8 mm; tarsal claws more gradually curved than in other Ephemerella species.  Let's have a look:

E. dorothea tarsal claw:

E. invaria tarsal claw:

Yes, they're quite different.   Beaty continues:

terga without dorsal tubercles but may have slightly developed spiculate protuberances...lateral margins of terga 4-9 with posterolateral projections; lateral margins with slight, small serrations with numerous setae.  

For the posterolateral projections and the setae on the lateral margins, we do not need a microscope photo:

But the lack of tubercles probably does require a close up:

Paired submedian "tubercles" are present on E. invaria nymphs on segments 3-8: those on segment 5 show up very clearly in this microscope photo:

Back to Beaty.  Thorax and abdomen variable in pigmentation, light brown to dark brown, with or without pale speckles; typically with paired posteromedial pale spots and sometimes with segments 5 and 6 pale mediad of gills; tergites may have a thin, pale mediodorsal stripe in some nymphs; caudal filaments banded.  

Well the pale stripe is very clear on the first nymph that I found yesterday, which was dark brown, while the "speckles" are clear on the second  -- though it could be argued that those speckles are dark!  These photos of nymphs found last year might be better for seeing "pale" speckles.

Our nymph does have "paired posteromedial pale spots" on the tergites, and there are pale areas on the sides of tergite 5 adjacent to the gills (note sure what "mediad" means?).

On the "super-sized" nymph at the top of the page -- dark brown with a prominent stripe -- this is a pattern I've not seen that often (though I found the same type of nymph in this very same stream at this time last year -- entry posted on 3/7/12).  Interestingly, Beaty notes at the end of his E. dorothea description: "Darker, unspeckled nymphs may be a subspecies or possibly a color variant of E. dorothea but DNA analysis and/or associations are necessary to confirm."  Maybe that would explain the unusual size.

While E. dorotheas may seem drab in relation to E. invaria and E. subvaria nymphs (again, look at the entry of 1/13), some do color up as they mature.  Witness this nymph from last year:


More photos from yesterday:

(Nice view of the "intersegmental setae" on the banded tails/caudal filaments.)

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