Oh they are eating it already. I didn't figure it could really hurt, and several of the breeding articles I've read suggest it. They say it gives somewhere to hide and crawl around, and that it helps prevent canablism. I've saw the bead box idea before, and thought about it, but I already had the film cans from another hobby of mine (geocaching), so I just went with them. Thanks for the suggestion though, if I didn't already have some of them I'd probably go for the box.
Sounds like they are quite a bit slower that the meal worms. I'm not sure exactly how long I've had mine, but I'd say around may, and my first babies are already getting close to 3/8 an inch. It seems like once they hit about a quarter they really start taking off quick. Good luck with the colony