Sleep seems obvious, especially when you hear your roommate snoring away like a didgeridoo.
But for some animals, it's a little harder to tell who's in dreamland.
Paper wasps, cockroaches, praying mantises, and fruit flies are among insects that doze. Fruit fly sleep is even similar to mammal sleep, since the flies respond to sleep-inducing chemicals and caffeine, just like people, Klein says.
Still, measuring sleep in insects is tricky—it's not always easy, for instance, to differentiate between sleep and sleep-like states.
Signs of true bug sleep are not moving, "drooping in the direction of gravity," and more relaxed muscles.
Another indicator is "increased arousal threshold," or how long it takes to jar the bug to alertness. (Take National Geographic's quiz on the secrets of sleep.)
Experiments in fruit flies also show that they experience "sleep rebound," Klein says. That means that a fruit fly deprived of sleep will subsequently need it more—something most of us busy people can understand.
Katy Prudic, a biologist at Oregon State University in Corvallis, adds that butterflies rest, "but we don't know if they sleep."
While butterflies rest in the evening, they also "can't move when it goes below a certain temperature," a state that looks like sleep but is a different type of dormancy called a torpor.
Bees Need Zzzzs
Butterflies "put themselves to bed" in the late afternoon, Prudic says, hanging from such hiding places as leaves, bark, or even beer cans.
Without adequate rest, they won't forage as well and females will lay eggs on the wrong plants for their caterpillar offspring to eat.
Just as sleep deprivation is a serious issue for humans, insects suffer from its consequences as well. In a 2010 study, Klein looked at sleep deprivation in honeybees, creating quite a super villainous sounding machine to do so: the insominator. (Read "Quest for a Superbee" in National Geographic magazine.)
In his experiments, magnets in the insominator disturbed the sleep of bees tagged with steel, while their nestmates, tagged with copper, got plenty of rest.
Bees inform each other about food sources and potential nest sites through a movement called a "waggle dance." The study showed sleep-deprived bees "behaved quite differently than bees with the more precise directional information."
For instance, the sleepy bees' dances were not as detailed—and thus not as helpful—as those of the bees that slept soundly. (Watch a video of a sleep-deprived bee dance.)
Show of hands for who's equally as sloppy after a Netflix marathon—and just named their TV "The Insominator."