There are really only two sources where the smell could come from: the fine excrements of the mealworms and the food that you place in the trays. Ideally, you will never overfeed your worms which should prevent any unwanted smell from rotten foods. The excrements are usually very dry which makes them almost odorless. Make sure you never feed too moist substances, then smell should be contained. The Hive has carbon filtration pads in the back and front of each growing tray though which air is ventilated. Therefore, occasional smells should be very well contained.