Goons Are Great posted:

In general most invertebrates or actually even most non-mammals sleep regularly, but not like we do in big blocks of sleep bound together over many hours, but split up over many, many moments of sleep across the day, combined with times of simple inactivity. Arachnids for example, especially Tarantulas and Scorpions (I also own a scorpion, hence why I take this example) are famous for their incredible inactivity throughout the day, just sitting there, doing literally nothing until hunger kicks in, they sleep a lot during that time, but not all the time, as you can observe when they react to you coming in, or moving a rock or whatever. Inaction is usually almost equal to sleep for many animals, especially invertebrates, so sitting around doing nothing is almost as good as sleep and a lot safer, as you can still react to stuff.
Ants do it just like that, too, they usually just sit around when exhausted and do nothing, which you can see inside the nest a lot. During those periods of low activity they also fall asleep from time to time, usually not for more than a few minutes, wake up again without doing anything, then fall asleep again etc.
They can adjust this almost freely in all directions, including sleeping and sitting around a lot when there's nothing to do, or being active for many hours at a time without any break. As long as the overall energy level is fine and there is enough food intake to generate energy (as with many invertebrates, ants cannot get fat or store food inside their bodies, so eating is a vital necessity and key to their ability to be active), they can but don't really have to sleep, however will still take every opportunity they can get just in case there is a time where this choice is no longer given.