Silkworms are an excellent substitute for crickets and other insects. They are high in calcium and protein and low in fat and exoskeleton so are easily digestible.
Silkworms should be fed either mulberry leaves or the silkworm prepared food once every day or they won't last very long. (never starved my worms so don't know how long it takes ot die if it isnt' fed. However, if they do not eat enough they will die when they shed their skins).
The silkworms themself if fed and kept clean (very easy to keep them clean, just put them on an egg carton or coffee tray, they won't move off it and y ou can tip it over and let all the poo fall out into a container then dump the poo out. Just make sure you pick up any worms that happen to fall into the bottom of the container. Change the carton every couple weeks once it starts looking soiled). I had about 300 silkworms, 1" long when I oredered them, last me about 2 months with just one bearded dragon to feed. He ate anywhere between 18-10 worms a day, the amount decreasing as they get older and unlike crickets you can feed them larger worms than the space between their eyes because of their soft bodies. (and well, they fold easier and easier to chew).