Hornworms do have mandibles, which they will use to bite. The small-medium worms won't do any damage, but the big ones pack a heck of a pinch that can definitely hurt your chameleon if it happens to latch on to a sensitive area. My cham found that out when he shot his tongue and grabbed the tail end first. The hornworm whipped around and grabbed right onto the skin of his neck area causing him to freak out, lol.
Very interesting information. I did not know that using small to med horns. Something to watch out for as they get bigger. Thank you.