Sounds like slugs, if there's a slimy trail.
Try some DE (diatomaceous earth) sprinkled around the plants. This should take care of them pretty quickly.
HTH
Susan

My first thought was slugs, but the trail looks like it's made of a web rather than slime up close. Also, the trail circles the plant a few times. I do have slugs around after this wet spring, but this doesn't look like any slug trouble I've had before (six years with this garden).

It also seems like quick work for slugs - literally overnight. The slugs have been working on my cucumbers' leaves, but they're not stripping the plants or significantly hindering their growth.

Planted a single pepper plant and used the DE last night - SUCCESS! The plant hasn't been chewed on at all. I guess it was the slugs!

Thanks, Susan!