I'm not sure what staghorn sumac looks like, but are you sure that's what the plant is? The caterpillar in the first picture is a question mark, and the two in the second picture appear to be also - they might possibly be red admirals.
The plant must be something in the Urticales order, like nettles, false nettles, elms, hackberry/sugarberry, and mulberries.
Question marks are beautiful butterflies!

{{gwi:444250}}

Sherry

Misssherry - you're right - those are elm leaves. Sumacs have compound leaves without the double teeth on the edges. If they have teeth, like staghorn, the teeth are simple.
Tucker

Miss Sherry is right. Those are question mark caterpillars. The plant is an elm, which is a favorite of the question mark.
Cheers,
Elisabeth

Thank you so much! I've gotten better at IDing trees, but I obviously still have a lot to learn. I'm really excited now! I've seen question marks before but have never had the chance to view them as well as I will, now that I have caterpillars. This is my first year raising caterpillars, and it's a whole new kind of fascinating. Geez-- I was expecting some kind of generalist moth. Thanks again!