Deep bins are to prevent the darned meal worms from climbing out. You would not believe how determined those worms are to escape their confinement. You'd tend to think they'd be happy hogs in heaven to be immersed in food 24/7. But no. They pile up in a corner of a shallow tray and use each other as "ladders" to reach the rim and then haul themselves out for a big adventure in the larger world. You do NOT want to experience the adventure of trying to wrangle a hundred worms humping their way across the floors of your house.
A deep bin might also help confine any grain mites as well, but those evil little tricksters aren't easily foiled by a straight-sided container. You really do want to keep your worm substrate as dry as possible if you have the least bit of humidity. I freeze my new substrate at zero F for at least one week before I use it. This will kill most of the grain mite eggs that come in the wheat bran.
A deep bin might also help confine any grain mites as well, but those evil little tricksters aren't easily foiled by a straight-sided container. You really do want to keep your worm substrate as dry as possible if you have the least bit of humidity. I freeze my new substrate at zero F for at least one week before I use it. This will kill most of the grain mite eggs that come in the wheat bran.
