All Kritter Keepers have well-ventilated lids in assorted colors and may be used as space-saving aquariums or insect havens, but are also ideal for use as small animal keepers, Kritter totes, terrariums or nurseries. Rectangular Kritter Keepers have self-locking lids with a hinged viewer/feeder windows Airline access hole and an attachment hole (except Mini and Small sizes) Mini, Small and Medium sizes have carrying handles for easy transport