In 2017, biologists showed that the upside-down jellyfish Cassiopea meets every criterion for sleep: at night its pulsing slows, it reacts more sluggishly, and if kept awake it dozes more the next day. Yet it has only a diffuse net of neurons and no brain at all. Sleep may therefore have appeared very early in animal evolution.
In 2022, a young tagged bar-tailed godwit flew from Alaska to Tasmania in about 11 days of nonstop flight, covering 13,560 km without eating, drinking or landing. Before departure, these birds pile on huge fat reserves and shrink their digestive organs, which are useless during the journey.
To escape rivals, a dung beetle rolls its ball of dung in a straight line. At night, it holds its course using the glowing band of the Milky Way. In a planetarium, researchers showed that beetles rolled straight under a starry sky but wandered aimlessly when the galaxy was switched off. It was the first animal known to navigate this way.