That does look like a rare one. I dont really know. You should wait for an expert.

>.>

Did you post on the butterfly forum? I've never seen anything like that - what state are you in?

Sumacs are tough - why not let the caterpillars live and tell us what they turn into?

That is a larval sawfly, probably Arge coccinea, a very nice looking insect.

Not to sound critical, but these larvae require foliage from sumacs (Rhus) to grow and develop.

Sawflies can be major plant stripping pests. My protective instincts have now been revoked.

I had some interesting ones last year, not the same kind. I left them alone. They defoliated a few plants but did not kill them.

torajima, these aren't caterpillars at all. Caterpillers develop into some form of moth, butterfly, or similar. The imaged critter is the larvae of a sawfly. They may LOOK like caterpillars, but aren't.

There are many different species of sawfly, some are incredibly beautiful or interesting as larvae!

I try not to interfere with the complex interactions of flora and fauna in my woodlands.Favoring one species over an other is not my goal.Unless there is a clear indication of an imbalance cause by human disturbances,such as an import,or unless I,m protecting something that I was planning to eat,I usually leave things alone.Finding a new insect is sort of like discovering a new wildflower,it's part of the enjoyment.My gardening goals are to promote biological diversity on my proprety,to encourge the self-emmergent complexity of the ecological balance,and to restore my yard to the symmetry of primeval nature.Anything less is crayons.