Wednesday, April 30, 2014

From the Oregon trip: the spiny crawler Ephemerella infrequens and some -- as yet -- undetermined Northern case-makers

We had a lot of rain in Portland last week, but I did get in a quick trip on Sunday.  My son-in-law took me to the Washougal River in Camas, WA.  The water (run-off, snow melt) was high, but we managed to find a few insects on the rocks close to shore.

For one, the spiny crawler in the photo at the top of the page, Ephemerella infrequens.  This is also called Ephemerella dorothea infrequens, and it's almost identical to the E. dorothea nymph that we're finding right now in the East.  Here's a close match: an E. dorothea that I photographed on 5/1/12:

Dorothea infrequens is described in the following way at under "Pacific Northwest Mayflies".  "Body uniform brown color, abdomen w/weak, light markings; no abdominal tubercles...small oval gills on segs 3-7."  (

The lack of the abdominal tubercles, and the "weak, light markings," are both clear in this microscope photo.  So too are the gills.

Not too tough to ID, and as you can see, both of the nymphs we picked up had fairly long wing pads.

E. infrequens in the West hatches as the "Pale Morning Dun" (PMD), while our E. dorothea here in the East is the "Pale Evening Dun" (PED).

Another easy one, a Green stonefly -- the only stonefly we found -- genus Sweltsa, the very same Chloroperlid we're finding right now in VA.  (We found two of them.)


And now for the problem child.  We found a bunch of caddis cases that were a mix of sticks and stones.  As it turned out, the main case was a cylinder made out of pebbles to which various sticks and pieces of wood were attached.  Here are photos of two of the larvae: note that the heads are totally black and therefore not easy to see.



There is no question at all that these are "Northern case-makers" (Limnephilidae): they have very prominent lateral and dorsal humps and very visible prosternal horns.  But that's as far as I've gotten so far.  I've spent the entire morning working through the descriptions and illustrations of Limnephilid genera in Wiggins (Larvae of the North American Caddisfly Genera) but I haven't nailed it down.  Frustrating.  If we have readers from the Northwest who recognize this one, please let me know.  The cases were found on rocks in slow water next to the shore.  The heads of the larvae are dark brown/black without any markings that I can see: the gills are branched, some with three filaments, others with two.  Any thoughts?  I'm happy to provide further details on anatomical features.

We're back in Virginia, and I'm anxious to get back to the streams.  But we've just had 4-5 inches of rain so it might be awhile.  Until then, I'll continue to work on the genus and species ID of those Limnephilids I found.

No comments:

Post a Comment