A Staff Report from the Straight Dope Science Advisory Board

Do insects sleep?

June 1, 1999

Dear Straight Dope:

Do insects sleep?

Doug Yanega of the department of entomology at the University of California at Riverside was kind enough to provide the following reply:

Short answer: Yes, but not the way we do. The vast majority of insects are active only during the day or only at night, and they will rest during their off-time. But is it "sleep"?

Long answer: Sleep in vertebrates is a complex physiological process, involving a number of very specific brain functions and hormones. In that sense, no arthropods have the same sort of sleep we do, since their physiology is almost completely different. However, there is a state called "torpor" that is the insect's equivalent of sleep.  If any vertebrates come close, it would be fish.  An insect in torpor exhibits immobility and distinctly reduced response to stimuli, though it can rouse from torpor in a matter of seconds if the stimulus is strong enough. Bearing in mind that there are already 1 million known insect species (out of an estimated 10-50 million), you'll appreciate that this is a generalization. There certainly are some insects, especially aquatic ones and those that live near the poles, that have different daily cycles or even maintain round-the-clock activity. Also, among insects that do exhibit torpor, the degree and nature of its expression is somewhat variable.

One of the more dramatic forms is seen in some bees (mostly in the family Apidae, and mostly in males) which will firmly clamp onto a plant with their jaws in the evening, and let go with their legs, which they then fold up. They hold this odd pose all night long, dangling in space, until they rouse the following morning. Many of the species which do this use the same spot every evening, presumably marking it with some chemical that they can detect from a distance, so they can find their way back. This very specific behavior is about the closest thing any insect has to conventional sleep.

Another special case is the New Zealand weta, a large flightless cricket relative, which lives at high altitude and freezes solid every evening, thawing out in the morning to go about its business. The wonders of antifreeze.

--Doug Yanega

SDSTAFF Dex adds:

I'm impressed--this came back within half an hour of my forwarding the question.   On the other hand, who amongst us could challenge someone who cites a New Zealand weta?

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