ID of first-instar larvae?

[Julie K. Stahlhut]

I found a cluster of about 40 pearl-gray eggs on quaking aspen (Populus
tremuloides) in Kalamazoo, Michigan.  The eggs hatched yesterday.

The caterpillars fed on their natal leaf by scraping, then began to
wander.  When I provided a fresh leaf, they silked the two leaves
together.  I haven't noticed any feeding behavior today.  (Also,
last night, they retreated to the base of the underside of the
leaf and seemed to anchor themselves to the base with silk.)
Even though they did wander on the first leaf, it looks like they're
gregarious at this stage; their leaf construction project has been
highly cooperative!

The larvae are now greenish and perhaps 2 mm long.  The closest fit
to the description of them that I can find is the Compton tortoise
shell butterfly (Nymphalis vau-album).  We have that butterfly in
this area, but I've never seen one in our neighborhood.

Does anyone have any other ideas on what they might possibly be?
--
Julie K. Stahlhut, Portable Curmudgeoness    julie.stahlhut at wmich.edu
 "Ever since he took up sex, I never see him."
               -- Attributed to Mrs. Kinsey