Unless you are extremely careless, they aren't getting out. They don't fly. I keep a screened lid on mine, not to keep them IN, but to keep weevil moths and anything else undesirable OUT. I have some in a shallow glass bowl (pupae) and they can't even crawl out of there.
I did see one trying to crawl up the side of the plastic container once but it had alot of dust matter on the side. It couldn't get past the screening (as in window screen material). I washed the container out and good as new and no one even made it half an inch up the side.
Preferably though keep them outside, perhaps in your coop. I have a bunch of mine in the wood shed right now as I am painting the coop floor for winter. They are stacked on top of each other in three layers of boxes while still allowing ventilation. Once again--they live on and thrive.
I did see one trying to crawl up the side of the plastic container once but it had alot of dust matter on the side. It couldn't get past the screening (as in window screen material). I washed the container out and good as new and no one even made it half an inch up the side.
Preferably though keep them outside, perhaps in your coop. I have a bunch of mine in the wood shed right now as I am painting the coop floor for winter. They are stacked on top of each other in three layers of boxes while still allowing ventilation. Once again--they live on and thrive.