horn worms cant be fed as much as silkworms. i was told don't quote me on this but if hornworms are fed to often some internal organ can tear (cant remember what one). thats what my pet shop told me and they're reliable.
Horn worms are a good treat but they grow too fast for my Jacksons. By the time I feed about half of them the other half are too big and I have to give them to my turtles. I have yet to try silks but they are next on my list.