venus fly traps are weird plants, you have to keep them in your fridge for a couple of months each year or they'll die off. they may make it to the second year, but they won't make it through a second winter. you can put them in a container outside as long as you can keep it above freezing and below 45. and they "like" anything that triggers them. touch one hair, they kind of prime themselves, touch the second hair, and they snap shut. they'll try to eat tweezers if you trigger them. not sure gnats are large enough to move the little hairs, they may be able to just walk around. same with mites, not large enough to move the trigger hairs
i don't know that much about pitcher plants, but as long as the gnats like the sweet "syrup" the plant exudes into the pitcher, they ought to work pretty well. might even work for mites, as long as they want the syrup, and not the plant itself
