Atmospheric beasts are cryptids or mythical creatures reputed to live high in the air and fly without wings because of being lighter than air. Cryptozoologists also call them biological UFOs, because some UFO sightings are supposed to be due to these creatures rather than alien spacecraft. The controversial substance called "star jelly" is alleged to be composed of the bodies of dead atmospheric beasts. Atmospheric beasts are sometimes explained as interdimensional beings, able to pop in and out of existence in a manner similar to ghosts, while other times they are thought to be fully natural biological organisms that are related genetically to terrestrial life and are built like jellyfish of the air.