Actually, I think most of the caterpillars attacking gardens this year are from moths. There have been gobs of moths this year due to the undecayed leaf litter from a mild winter with very little snow.

Sawfly larvae most likely. They will turn into an ugly tan and black, wasp looking flying pest and nuisance. Pick the bugs off and squash them gleefully. If you look closely further down the cane of the rose, you will likely see a black section and lesion. This is where the larvae hatched from. The adult sawfly lay's eggs right into the tender new rose canes and these worms hatch from there and eat all the tender new growth and buds. They are a nuisance here at this time of year.

A picture would be helpful, once you have that, post it on flicker and ask an ID group, such as Forest and Kim Starr, who is an expert in Hawaii's flora and fauna.

Rose slugs, the larva of a sawfly. Control is with hand squishing, Insecticidal Soaps, Neem oil in that order. I had them on my roses until I got the soil into a good, healthy state so the roses that grew there were strong and healthy and I've not seen them on the roses for several years. I have had them in the past on the Hibiscus, but not this year.