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

Barred from her lab by pandemic restrictions, behavioral ecologist Daniela C. Rößler 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. Rößler and her colleagues wondered if the twitching spiders could be experiencing something like an REM phase of sleep and possibly even having dreams. Though most spiders cannot move their eyes even while awake, jumping spiders have long tubes that shift their retinas around behind their large principal eyes. It is too soon to say for sure that the spiders are experiencing something akin to REM sleep in humans, Klein cautions. 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. So if spiders dream, "It might mean that we start talking about spiders having something like a minimal self," says Peña-Guzmán, who was not involved with the spider research. Rößler also wants to look for REM sleep in other spider species and points out that it might look very different in animals that rely more on senses other than vision, such as spiders that use vibrations in their webs to detect when prey is caught.