If they're not damaging anything, not to worry.

That said, can you post pictures?

Yes let me read up on how to post a pic.

Many mature caterpillars are out and moving around to find some place to spend the winter, they are done eating and will not cause any more damage. Most will end up as food for some predator although some may safely make it to the pupating stage, and even then they can be food for many birds over the winter. So there is no real reason to spray something to kill most of these caterpillars, now.