Thank you to everyone who responded to my problem, both here at Mid Atlantic and the Heuchera forums. A couple of people suggested different kinds of beetles as likely suspects and that seems the most probable suggestion to me. Perhaps I should move all the heuchera, about 20 or more of them both large and small to another location. Then plant more astibles and ferns that have not been disturbed so far in the problem location
When you first posted about your heuchera being eaten by something other than the usual suspects, I immediately thought of two new to me suspects in the last three years that have caused similar damage in my yard. I'd like to suggest you research winter moth. It's the little green inch worm type caterpillar that is defoliating trees and then drops down on thread like strands to eat what even they land on below. Here, roses. shrubs, heucera, blueberries, Japanese Maples, hydrangea, coleus, etc.
Here is a thread from 2009 that mentions damage to the heuchera from winter moth
The eggs will be hatching soon. If your coral bells were eaten before mid June, I'd strongly suggest winter moth as the culprit My eaten down to the stems and veins Georgia Peach did live, but it is half the size of the other that didn't have to regrow!