On Saturday, as I looked through my reference vials, I discovered a pair of Limnephilids (Northern Case makers) that I had found years ago in the Whippoorwill Branch of the Mechums (one was in the case in the photo above). I had identified them to the level of genus -- Pycnopsyche -- but not to the level of species. Decided to give it a try. I concluded that they were P. scabripennis, but I thought I'd check in with Beaty. Without seeing the larva, he said that the case looked like that of P. luculenta. Well, back to the drawing board.
I began by looking at Beaty's description of P. luculenta. ("The Trichoptera of North Carolina," p. 85)
P. luculenta -- larvae 20-22 mm; head yellowish, dark spots mostly distinct, ventral margin of posterior femora with 3-4 major setae; venter of first abdominal segment with more than 15 setae. Case a distinctive, slightly flattened cylinder of plant materials with long sticks laterally extending posteriorly. Common.
Kind of a perfect description of the case. But let's look at the larva.
1. Pycnopsyche -- single abdominal gills.
2. Pycnopsyche -- long sclerite at base of posterior of lateral hump.
3. Pycnopsyche -- metanotal sa1 sclerites not fused.
Good to go on the genus. On to the species ID.
1. Size of the larva? Mine was 20 mm so that fits.
2. Head color and pattern look right.
3.Ventral margin of the posterior femora -- are there 3-4 major setae? I'd say that there are.
4. The case we've already cleared. But what about the setae on the first abdominal ventral segment? I see a total of, maybe 10 setae, and most are very small.
Now that looks like a problem. There clearly are not more than 15 setae on the first ventral abdominal sternum. However, when Steve wrote to me yesterday, he sent me a new key on Pycnopsyche, part of a new book that has just been released: John C. Morse, W. Patrick McCafferty, Bill P. Stark, and Luke M. Jacobus, Editors, Larvae of the Southeastern USA: Mayfly, Stonefly, and Caddisfly Species (Clemson University Press). (I immediately put in my order!) Let's see what we get using that key.
230. .... case cylindrical, constructed of stones only........231
230'; .... case cylindrical or depressed, constructed of plant materials or of sand, or stones and often with plant materials..........232
We move on to 232.
232. Ventral margin of each hind femur with 3 or more major setae.... 233
232'. Ventral margin of each hind femur usually with 2 major setae.... 234
We've already seen that there are 3 or more major setae on the hind femur. On to 233.
233. Abdominal sternum I with 12-17 anterior (sa1) setae (mostly very small), 6-7 setae on each posteromesal (sa2) sclerite, and 6-8 setae on each lateral (sa3) sclerite....Pycnopsyche divergens
233' Abdominal sternum I with 3-11 anterior (sa1) setae (mostly very small), 3-6 setae on each posteromesal (sa2) sclerite, and 2-6 setae on each lateral (sa3) sclerite; case depressed in cross section and with 1 or more long sticks along sides...........streams........... WI to QC south to AL, GA, KY, MS, NC, SC, TN, Pycnopsyche luculenta
The case is a match for P. luculenta. So too is the number of setae on abdominal sternum I. What about the number of setae at positions sa2 and sa3? Two microscope photos.
I can see 2, possibly 3, setae on the lower lateral sclerite. Have to say that if we use the new key, we key out, indeed, to Pycnopsyche luculenta. I'll send these larvae to Beaty in a couple of weeks -- when I return from Montana (: to see what he thinks. But I feel pretty good about that ID.
One more thing, I have pics of another larva I found in another small stream in Sugar Hollow that also looks like P. luculenta to me. Very cool.
While I was working on this yesterday, I decided to use the new key to see what I could find out about the many Limnephilids I've found over the years at the Rapidan River. Here are pics of a few.
I could go on. I seem to find 1 or 2 every year. Using Beaty's description ("The Trichoptera of North Carolina," p. 85), I had concluded, with reservations, that these were all Pycnopsyche scabripennis. I say reservations because he says that there are less than 15 setae on the "venter of [the] first abdominal segment": I always see more. (More than 20, by the way, would lead to an ID of P. guttifer, but that's problematic. P. guttifer is said to be found in "large, warm streams": that doesn't describe the Rapidan River at all.)
Let's use the new key. As we did before, we can move to 232 from item 230.
232. Ventral margin of each hind femur with 3 or more major setae.... 233
232'. Ventral margin of each hind femur usually with 2 major setae.... 234
Let's see what we've got. (I'm using the larva in the last photo above.)
In this case I'd say there are no more than 2 major setae on the femur. On to item 234.
234. Case mostly mineral; in .....lowland streams.. or possibly spring brooks... or lakes and streams (that's clearly out)
234' Case of plant material; in
...... small to moderate streams
..... or small to medium rivers (that includes P. guttifera)
..... or larger streams & rivers
..... or possibly spring brooks
.... or cool, moderate-size streams ..... Pycnopsyche scabripennis
.... or lowland streams
The Rapidan River is, without a doubt, a "cool, moderate-size stream."
Think my previous ID can stand. Can't wait to get that new book!
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As noted above, I'm off to Montana for a week of fishing and insect collecting. Next entry will be a report on those findings.
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Should note, by the way, that I'm not sure that all of the Rapidan Limnephilids I've found were P. scabripennis. I have found some with cases that look a lot like P. luculenta. Unfortunately, I can't check them since I no longer have the larvae.
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