I think it could have been caused by lack of water and diet possibly. I think 10-20 superworms a day is excessive. I would start feeding him insects every other or third day and give him salads every other day. Use mustard, turnip, endive etc and add some shredded carrots and other veggies with a little fruit. This will provide water to him if he isn't a big drinker. Also try some warm shallow soaks maybe once every two weeks.

Good luck