Collected in Maryland on 4/30/2010 along with many sawfly larvae feeding on what I think is chestnut oak. I didn't notice that one of the larvae was actually a caterpillar and not a sawfly, but it is lighter in color and is growing faster than the sawflies. When I first saw it around April 30 it was the same size as the sawfly larvae, around 7-8 mm.
I am feeding them leaves of red oak although I am sure it is not the same species on which I found them.
Carnivorous caterpillars
See