I don't, off-hand, think I've had anything eating holes in my pelargonia
in years, but I've found green caterpillars making lace of two of my
outdoor potted ones this year. They look very much like the small white
butterfly larvae I squash on my brassicas, but I haven't yet caught two
at the same time so that I can compare them.

I find from Wikip that the Angle Shades moth is a possible culprit, but
the larvae I've executed didn't really match the picture at:
http://en.wikipedia.org/wiki/Angle_Shades

If this is it, could I be in for some long-term grief? My little Gem
Guide says it eats, throughout the year, almost any herbaceous plant,
and Wp says it overwinters as a larva.

--
Mike.