You might sleep, and dream, like a spider

The next time you spot a spider hanging upside down in your apartment, it might actually be snoozing somewhat like humans.

Behavioral ecologist Daniela Rößler made this accidental finding when she first observed jumping spiders dangling in her laboratory in 2020. Rößler and her research team recently published their findings in the journal Proceedings of the National Academy of Sciences. 

Rößler, a researcher at the University of Konstanz in Germany, originally set out to study predator-prey interactions in spiders. She used baby spiders for her experiment, and opportunistically filmed the animals at night using an infrared camera.

The spiders exhibited something like rapid eye movements (REM), a behavior we and many animals often experience when sleeping. During REM, activities in the body such as heart rate escalate, while the eyes remain closed and move rapidly.  

This Tweet is currently unavailable. It might be loading or has been removed.

While watching the spiders, the research team also observed the animals occasionally twitching their limbs, another classic REM behavior. Together, these findings suggest that a dreamy, sleep-like state could exist in spiders. There is already evidence fruit flies sleep. But this is the first time the REM pattern was documented in a jumping spider, said Rößler. 

But what looks like sleep to us may or may not be sleep in spiders. Though the research team’s findings very much suggest that spiders do sleep, the evidence isn't yet certain, noted Rößler.

As an extension of this research, Rößler is planning to conduct sleep studies in a field atmosphere as opposed to capturing spiders and studying them in an artificial lab environment. "If we really want to understand the function of sleep, we need to look at it where it happens," she explained. 

Yet the lab setting still produced compelling results. It is a well done study that has documented twitching in spiders, said Mark Blumberg, a professor at the University of Iowa who researches twitching and REM sleep in rats and human infants. Blumberg was not part of this newly published study. 

Want more science and tech news delivered straight to your inbox? Sign up for Mashable's Top Stories newsletter today.

Blumberg acknowledged that it's tricky to study sleep in animals, because animals may experience sleep differently than us. "I agree with much of the study. I don't agree with everything about it," Blumberg told Mashable. The nervous system of a spider or fly is very different from that of a rat or a human, and so we cannot expect all features of sleep to be similar in spiders, he emphasized. 

Rößler’s study touched on the possibility of spiders dreaming during sleep, thanks to the eye movement patterns the arachnids experienced in REM sleep. During REM sleep, vivid hallucinogenic dreams occur in humans. The new study raises the potential of studying the existence of visual dreams in spiders. But in Blumberg's view, the dream connection is too uncertain, and unconvincing. 

For Rößler, dreaming in spiders also remains a big question. She hopes to better understand if humans can even fathom how a spider might dream, if they dream at all. "We always have this human bias in trying to understand the world," she said.

There’s still a lot to unearth about sleep in animals. But more insights may be on the way. "I think we're gonna find amazing things in the next couple years," Rößler said.