I think what you're dealing with are Pear Slugs, which may or may not be what Beeman mentioned above. I used to see them on my pear trees and would just squish 'em when I found them. I don't see them anymore. In small numbers they didn't seem to do much damage, just mining the leaf surfaces here and there. They are a serious pear pest though in other parts of the country. Here is a link that might be useful: Pear Slugs

I'm pretty sure they're orange striped oakworms. Oakworms always show up in groups, but I've never seen so many on a tree at once that the oak was defoliated. Sherry

Thanks for the response. I actually went to google first and came up empty handed. I even came across the key you linked to and was unsuccessful. Perhaps I should give it another try.

Thank you again! I am actually fascinated by this caterpillar. Visited it today and was amazed by how well it blended in with the leaf. Plus I just noticed the funky “face” on it’s back end.