So here are a few pictures we took of different sized caterpillars while Dad held a tape measure next to them. Pictures are from 4:30 pm on Saturday, so by the time this posts they will be bigger.
We think this guy is the biggest of all of them: there seemed to be several about 1 1/2 inches long, but he seemed the very longest.
A slightly smaller one (sorry for the focus).
These next two must have hatched later than the biggest ones. You can see this guy is not even 1 inch.
And THIS little fella is about 1/2 inch long.