Oh yeah, if it was something like a hornworm it would eat all of the leaves overnight and leave the branches sticking up like a dead tree. That definitely looks like damage from something much, much bigger. One picture seems to show a fairly thick stem with a ragged edge like it has been chewed on. My first thought was deer, but you say you're in the 'burbs, so probably not deer. Next culprit on my list would be dogs or cats. Don't know many dogs that would eat oregano, but cats will definitely eat it (I have to grow catnip and sweetgrass specifically for mine to keep it out of my peppers and houseplants). The good news is that pepper plants are virtually impossible to kill by pruning (or in this case chewing), they'll redouble their growth and be right back to where they were in a week or two. Probably better in the long run because they'll bush out more, make the plant more stable and wider so it sets more fruit. Might be a blessing in disguise for you.

Cut back on watering and the larvae will die...they are the ones who feed on the roots of potted plants. BT dunks will also work on them.

aseedisapromise, lol, yes, my screen name is only based on my love of prairies and meadows and moons. I'm from the Boston area, MA is for Massachusetts. I've never been to Kansas. California is the only area I've visited outside of the East Coast. I guess I might have flown over Kansas, if that counts. (g) One of my favorite movies was 'Oklahoma' which is next to Kansas, mostly for the beautiful soundtrack not the plot. I suppose most of my geographical impressions of the midwest come from that movie though. Agriculture, corn fields, ranches. But you are in South Dakota? Which is another state I've only heard about. Seems like a challenging climate in the winter, yes? Are you affected by the drought conditions too? As for zones, I guess in my mind, Kansas is somewhat more south than Massachusetts so I just expect a warmer zone anywhere South of me, which is just not the case. It isn't like there is a line separating the north of the country from the south, it's more like a curve I guess. And I am a little warmer than many areas very close by me. Zone 5 is more prevalent here with a little of zone 7 on the Cape and the Islands. And I love your screen name. It is so true...a seed is a promise. I've always enjoyed starting plants from seeds and it is amazing when you think about it. This post was edited by prairiemoon2 on Mon, Sep 9, 13 at 11:12

Tomato leaves get hit by hail (ask anthony_toronto) and devoured by hornworms with some regularity. The vines respond by putting out new growth. If your plants have good, healthy root systems, they'll probably bounce back. Yes, you've lost some time. Also, IIRC, cutting off too much foliage at once rather shocks the plant. But I can't remember how the plant is affected. Is there a lot of fruit on the plants? What percentage of the leaves did you remove?