Superworms are fine to give to an adult dragon 2-3 times a week. However, as many posters have already stated, variety is the best thing to give your dragon. Crickets, superworms, silkworms, roaches, hornworms, etc as well as a wide assortment of greens (collard greens, dandelion greens, endive, escaroli, mustard greens, bell peppers, zuccini, string beans, corn, peas, squash, pansey flowers, hispiscis (or however it's spelled), dandelion flowers, mangos etc. THe website provided by another poster has a great nutrition chart to use)
Spinach, though high in iron and calcium is dangerous to feed to dragons. It contains a high amount of oxates which bind with calcium and make it unusable to the dragon. The high iron content can cause problems too, I beleive. Thus it is safer to just leave it out of the dragon's diet completely.
Kale, also very high in calcium is a little too high in phospherous which can cause problems in dragons. However small amounts of kale is a good addition to the dragon's diet but should not be used as a stable green. (ie fed every day)
Collard greens, dandelion greens, endive, escaroli, mustard greens, these are great every day greens to use. You don't need to use all of them every day, but using 2 or more daily (you can rotate amoung them ever week etc, to keep things interesting for your dragon and help keep them from getting picky). Of course two greens isn't enough but that is when you add the other greens, vegetables/fruit/flowers to 'spice it up'. Just keep the stable green about 50-60% of the total salad.
The main reason a variety should be offered to all pets that are not food restricted (ie can only eat one or two kinds of food, such as snakes (many will only eat rodents, some only other reptiles, insects, fish, birds, eggs etc), horned toads (almost all are exclusively ant eaters), etc. Being omnivorous bearded dragons need that variety of food stuff, to ensure they are getting good nutrition in the quantities they need. Of course we can help balance 'bad diet' with multivitamins and calcium powders but it is very difficult to know how much is too much and how little is too little. (what I mean by 'bad diet' is not what we actually feed them but because we, here in North American and other areas outside of Australia cannot get or accurately replicate what bearded dragons eat in their native habitat). But all we can really do is do our best to give as much variety as possible.
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PHLdyPayne