Hi Janet,

Without pictures, a description of the caterpillars, or knowing what the host tree is, I have no way of knowing what the caterpillars are. But they are most likely not a problem for your trees. Caterpillars are well controlled by a variety of natural enemies (birds, paper wasps, parasitic wasps, etc.). Caterpillar damage to trees is often insignificant. And even if there is a high population this year, that is unlikely to persist year to year.

Let me know if you have further questions.