Spiders sleep, and not in a simple way. A new study in Proceedings of the National Academy of Sciences reports that jumping spiders cycle through two distinct sleep stages, one of which looks a lot like REM sleep in people.
The team, based at the University of Bonn in Germany, studied Portia fimbriata, an Australian jumping spider about the size of a one-euro coin. The genus is known for hunting other spiders, often by imitating the vibrations of trapped insects.
How they tested it
Researchers kept individual spiders in small dishes and filmed them overnight with infrared cameras. They tracked sleeping posture, long stretches of stillness, and twitching movements. They also played sounds to see how readily the animals reacted, a way to tell real sleep from simply sitting still.
Finally, they disturbed some spiders’ rest. Those animals later made up for it with extra sleep, a “rebound” effect that is considered a hallmark of regulated sleep in other animals.
What they found
The spiders showed two distinguishable sleep stages. One resembled human REM sleep, with eye movements and muscle twitches. The authors describe the results as the first comprehensive experimental confirmation that spiders have genuine, regulated sleep rather than plain inactivity.
That matters because sleep is usually studied in animals with backbones. Showing it in a spider suggests that sleep, and perhaps sleep stages, may be far more widespread among animals than once assumed.
The catch
Don’t picture a spider dreaming just yet. The researchers stress that REM-like movements do not show whether spiders dream. The team also did not measure brain activity; the sleep stages were identified from behavior alone. And because spiders sense the world differently than people do, it took effort to find a sound that reliably prompted a response.
Next, the group plans to compare sleep across spider species, contrast lab and natural settings, and look at links between sleep and thinking. It also wants to test how climate change and artificial light at night affect the sleep of spiders and their relatives.
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