Waxworms would make a yummy treat, but not often. They are packed with protein and too much can cause constipation. I don't know how tasty silkworms would be to a fish. You can always give it a try if you can get a sample of just a few worms instead of a whole culture. I know my lizard doesn't seem to care for them much. May have something to do with the texture of the worm. Waxworms have a silky smooth body whereas silkworms are bumpy and sort of powdery.