I've kept them for about 6 years now and keep finding more around my house, friends' houses, parks etc. It seems that sometimes the nymphs decrease in number as they get older, perhaps they cannibalize or escape, I can't figure it out, but few reach adulthood. Perhaps they need a larger container? They love oak leaves, I can almost always find dozens hiding around oak trees here. I notice they also seem to do better in dryer habitats and I find them mostly in dry, but dark areas.
I also adore their chemical defense odor... probably one of my favorite smells! But man it stinks like nothing else after they die...