Is this caterpillar harmful?
I have seen lots of these caterpillars in my garden over the past week or two. Often they are on the milkweed, but not eating anywhere near as voraciously as the monarchs. Today I saw one feeding on a penta plant. I have not been able to identify this from researching online, and would appreciate any help you can provide.
Looks like fall webworm. They are wandering around now and looking for someplace to pupate for the winter. Not doing any significant feeding damage. This is a native caterpillar that provides a lot of food mass for birds and other wildlife. We don't recommend any measures this late in the season.
You can search fall webworm on our website for more information about fall webworm.