Spiders Seem To Have REM-Like Sleep and May Even Dream

An anonymous reader quotes a report from Scientific American: Barred from her lab by pandemic restrictions, behavioral ecologist Daniela C. Robler caught local jumping spiders and kept them in clear plastic boxes on her windowsill, planning to test their reactions to 3-D-printed models of predatory spiders. When she came home from dinner one night, though, she noticed something strange. "They were all hanging from the lids of their boxes," says Robler, a postdoctoral researcher at the University of Konstanz in Germany. She had never seen jumping spiders suspended motionless on silk lines like this before. "I had no idea what happened," Robler says. "I thought they were dead." It turns out the jumping spiders were simply asleep -- and that Robler had discovered an alternate sleeping habit of the species Evarcha arcuata, which had been known to build silk sleeping dens in curled-up dead leaves. But the real surprise came when she decided to spy on them all night. [...] Mostly the spider just hung there. But then her legs started to twitch, and her abdomen and even her silk-producing spinnerets did so as well. Sometimes her legs curled in toward her sternum. With every spider Robler recorded, these odd movements only appeared during distinct bouts that lasted a little more than a minute and occurred periodically throughout the night. "They were just uncontrollably twitching in a way that really looked a lot like when dogs or cats dream and have their little REM phases," she says. [...] Robler and her colleagues wondered if the twitching spiders could be experiencing something like an REM phase of sleep and possibly even having dreams. "We were like, 'Okay, that would be insane,'" she says. Then she thought, "Let's figure it out," and immediately changed her research plans for the spiders. [...] When Robler recorded 34 sleeping spiderlings, she found that their twitches were accompanied by unmistakable eye-tube movements that did not happen during other phases of sleep. [...] But it is too soon to say for sure that the spiders are experiencing something akin to REM sleep in humans. The researchers first need to confirm the spiders are actually asleep during this phase by showing that they are less responsive to their environment. Robler and her "dream team" of co-authors have already started those tests. And she points out that the leg curling is a particularly striking aspect of the spiders' REM-like phase because that pose is typically only seen in dead spiders. Spiders use hydraulic pressure maintained by muscles to keep their legs extended, and the curling could result from the muscle paralysis that typifies REM sleep. The team's initial findings were published in Proceedings of the National Academy of Sciences USA.

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