Do spiders sleep? Study suggests they may snooze like humans
It’s a question that keeps some scientists up at night: Do spiders sleep?
Daniela Roessler and her colleagues trained cameras on baby jumping spiders at night to find out. The images showed patterns that looked a lot like sleep cycles: the spiders’ legs trembled and parts of their eyes flickered.
The researchers described this pattern as an “REM sleep-like state.” In humans, REM, or rapid eye movement, is an active stage of sleep when parts of the brain light up with activity and is closely associated with dreaming.
Other animals, including some birds and mammals, have been shown to experience REM sleep. But creatures like the jumping spider haven’t gotten as much attention, so it wasn’t known whether they got the same kind of sleep, said Roessler, an evolutionary biologist at the University of Konstanz in Germany.
Their findings were published Monday in the journal Proceedings of the National Academy of Sciences.
Roessler and her team got into the sleep issue after discovering that the spiders hung by silk threads in their lab containers at night. She had recently scooped up a pair of jumping spiders to study, a common species with a hairy brown body and four pairs of large eyes.
“It was just the most unusual thing I’ve ever seen,” Roessler said of the hanging spiders.
The study showed that the spiders’ nocturnal movements were much like REM in other species, she said, such as dogs or cats twitching in their sleep. And they happened in regular cycles, similar to sleep patterns in humans.
Many spider-like species don’t actually have movable eyes, making it difficult to compare their sleep cycles, explains co-author Paul Shamble, an evolutionary biologist at Harvard University.
But these jumping spiders are predators that move their retinas to change their gaze as they hunt, Shamble said. In addition, the young spiders have a translucent outer layer that provides a clear window into their bodies.
“Sometimes as a biologist you’re just really, really lucky,” Shamble said.
The researchers have yet to figure out whether the spiders are technically asleep while in these resting states, Roessler said. That includes testing whether they respond more slowly — or not at all — to triggers they would normally activate.
Critters like the jumping spider are very far removed from humans in the evolutionary tree. Jerry Siegel, a sleep researcher not involved in the study, said he doubts the spiders can truly experience REM sleep.
“There may be animals that have activity in quiet states,” says Siegel of the UCLA Center for Sleep Research. “But are they REM sleep? It’s hard to imagine they could be the same.”
But Barrett Klein, an entomologist at the University of Wisconsin-La Crosse who was also not involved in the study, said it was exciting to find REM-like signs in such a distant relative. Many questions remain about how widespread REM sleep is and what purpose it may serve for species, he said.
REM sleep is “still a black box,” Klein said.
Daniela C. Rößler et al, Frequent attacks of retinal movement suggest an REM sleep-like state in jumping spiders, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2204754119
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