I bought one of those small cricket keepers from the pet store, so there are slits in the top for airholes. Somehow, the really tiny crix find a way to escape through these slots. What could I do to prevent their escape without cutting off their airflow?
You could check the hardware store and see if they have any really fine mesh. Then glue the mesh over those vents on the inside of the keeper - air will still go through but the mesh should stop crickets from fitting through.