You think they are working 24 hours a day because you see them working at every wakeful hour. And all the workers look the same. But no one knows whether ants “sleep”. They don’t have eyelids, so they can’t close their eyes. But they do have periods of rest, where the brain and biological functions slow down and they stop moving. Though not well documented and possibly varying from species to species, it is generally accepted that most ants have periods of dormancy akin to sleep.
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As workers, ants have to respond to the colony needs. Ants seen foraging for food work from sunrise to sunset. Others inside the colony do other chores like tending to the queen and raising the larvae. The whole colony does not ‘sleep’ at the same time. They have “shifts” — one ant takes up the responsibilities, relieving another which can then tend to its own needs like sleep and feeding itself. Once inside for the night, ants reduce their activities. They fall in a sleep-like idleness with reduced biological functions. Each ant rests (a way of preserving resources) when necessary and “wakes up” when the colony needs it again, but the ants need time to get to normal functioning, resulting in a sluggish movement.