The
earthworm, one of nature's most nutritious foods, is 70 percent
protein and low in
fat. It's high quality protein, containing a wider variety of
amino acids than beef. Earthworms can eat virtually any sort of
organic material, making them ideal for recycling waste products.
Though worms are raised commercially by a process known as vermiculture, their uses are generally limited to bait, and occasionally animal feed. There's actually a considerable amount of research being done on the second of these uses, which has not yet become economically viable on a large scale.
The use of earthworms in certain fast food products is strictly an urban legend. In Korea, however, where much of the earthworm research is being done, earthworms were once consumed for stamina under the name toryongtang. You'd never be able to pass a Diet of Worms on a human being who knew what they were eating, but chickens and catfish wouldn't mind it at all. If new processes can be developed to lower the cost of earthworm meal, you might be (indirectly) consuming worms at KFC in a decade or so.