Sunday, March 9, 2014

On that free-living caddisfly larva -- could it be Rhyacophila shenandoahensis?

The Rhyacophilid I found yesterday at Entry Run in Greene County -- the one in this photo -- might be Rhyacophila shenandoahensis.  Should that turn out to be true, this would be quite a find.

R. shenandoahensis appears to belong to the R. banksi complex of the R. invaria group -- on which see the entry posted on 1/28/14.   Like other members of that complex, our larva does not have an apicolateral spur, lacks a basoventral hook, and has two ventral teeth on each anal claw.

R. shenandoahensis was described by Oliver S. Flint, Jr. in his article, "Larvae of the caddis fly genus Rhyacophila in Eastern North America,"  Proceedings of the United States National Museum, 113:3464 (1962), pp. 483-484.   Before I read parts of that description, have a close look at the head of our larva.

Flint.  "This species has been collected only in the mountains of Shenandoah National Park and those nearby."  (Sure helps our case.)  "Description: Length, 16 mm.  Head, brownish yellow, marked with deep brown, both mesodorsally and ventrally; muscle scars pale, inconspicuous, head capsule slightly wider posteriorly, apex of frontoclypeus blunt."  (I don't have a photo of the ventral side of the head; the rest seems to fit.)  "Thorax, pronotum, yellow, with dark oval mark posteromesally [i.e. back middle]; fore femora much broadened.  Abdomen, anal proleg with short basoventral and apicolateral processes, not free of membrane [i.e., neither sticks out]; claw with a second small ventral tooth."

I think the head and pronotum of our larva match the description supplied.


In his remarks, Flint reiterates the close connection of this species with the SNP.  "The larvae of this species seem to be the only ones of the genus in the small brooks and springs of the Shenandoah National Park."  Some of the places where this species is found: Hogcamp Brook (not far from Entry Run), Skyline Drive, Milepost 71.5, Skyline Drive, Milepost 79.5, even near Waynesboro.  We're right in its domain.

However, two points made by Flint work against this ID for our larva.  1) "The larvae were not collected in brooklets more than a yard wide, and were often found in the leaf packets in the small springs."  I did indeed find this larva in a leaf pack, but Entry Run where I was looking was certainly wider than a yard.

2) "Although the larvae were not collected in the fall, they probably do hatch before winter, inasmuch as the larvae are nearly full grown by early March."   The larva I found was far from being "full grown"; it was only 8-10 mm.

So, we can't be sure we found R. shenandoahensis  -- but it's still an ID to consider.  Since even the pros can't really distinguish the species in the R. banksi complex from one another, this is the best we can do.   It's nice to live near these mountains where the Rhyacophilids abound!


(Oh.  R. shenandoahensis has been found in Canada (Ontario) and Virginia.  In Virginia it's listed as "vulnerable."  See:

No comments:

Post a Comment