Worms can be highly addictive to chams, which is why most will feed them as treats a couple of times a week. I would recommend adding more variety to his diet, so he doesn't grow tired of eating the same feeders. You have silkworms, hornworms, roaches, butterworms, phoenix worms, etc.Also, don't be afraid to take away his food altogether for a day or two if he's being picky. They can go for weeks without eating anything as long as they are hydrating.