Fruit Fly Bottles are a great invention! I use them for House Fly & Blue Bottle Pupae. I put the amount of pupae I want to hatch in the bottles and shake them down to the bottom layer, when they hatch the flies crawl to the upper layer & I just place the bottle in the feeding hole and the flies walk into the containers just in time to be dinner! The photo on the right is showing 3 bottles in three holes, they have a lip which holds itself into the 1 1/2" hole I drill into the mantis containers! Of course they are also used for culturing fruit flies! I just find them more useful as feeder bottles!