Do flies sleep?
The quick answer is yes. The long answer can be found here.
I have dealt with sleeping flies in the the past. Not as an entomologist, but as a pet owner. When I was young my brother had a small rainbow skink. It loved to eat flies. But the flies had to be alive and moving. So I became a fly catcher. My prey: Muscid flies, aka house flies. I figured out how to sneak up on them. Early in the morning they could be found on flowers on the sunny side of the house. I remember waving my hand in front of them and they didn’t move. They just stood there with those big eyes, not seeing me. Asleep. I’d scoop them up in paper cups and release them in the skink tank. Easy.
Recently a cluster fly decided the kitchen was a good place to spend the winter. It found a crack between the sill and the wall. This fly was looking for a sleeping spot for the whole winter. This type of long dormant sleeping in insects is called “diapause”. During this time they don’t move much, they will drink if water is available. They don’t feed, no mating, not much in the way of flying, unless it gets unseasonably warm and they think it is spring.
Not just flies fall into this overwintering stage, squash bugs, lady bugs, bees, wasps and even mosquitoes do it.
I get countless calls during the fall and early winter about bugs in peoples homes. They come in with the wood, or they fly in looking for a dry, warmer than outside spot to curl up for the winter. Not a bad strategy. I kind of wish I could do it too as long as I had a pile of good books.