Hickory Horned Devil -- Citheronia Regalis
What a find! These demonic looking caterpillars drop down from the trees to find a place to burrow & pupate in late summer.
If you look closely, you'll notice this isn't the same one as the first two photos. This one has black horns, I found him last August whereas the one with orange horns I found yesterday.
Maybe the larger, light teal with orange horns one is female and this one is male? I wonder...
As caterpillars don't need to find/attract sexual partners, I guess there is no need for gender dimorphimsm at this stage of development (that doesn't mean I would completely exclude this explanation).
In Wikipedia I find: "They molt four times. Each instar is different, but on their fifth and final instar they become a bright green color, with huge, black-tipped red horns, earning them their common name hickory horned devils.".