I use caterpillars a great deal as they are soft bodied and packed with high energy nutrients. However, I would do not feed any caterpillars which are hairy or brightly coloured as these are sure signs of potential toxicity. Some smooth, camouflaged caterpillars are able to exude an unpalatable liquid from their mouth and I'd not use these either. You can determine which ones do this simply by squeezing them slightly with forceps.