Some spiders can enter REM sleep – and possibly even dream, study finds
A new study, led by German, Italian and American researchers, indicates that a species of jumping spider may have another fascinating trait: the ability to have rapid eye movement sleep, a resting phase characterized by contractions limbs, high brain activity and eyes that race in different directions. Scientists say humans have their most vivid dreams during REM sleep.
“There was no way in my life that I would have thought that [jumping spiders] could have something like REM sleep,” Daniela Roessler, a behavioral ecologist at the University of Konstanz in Germany and lead author of the study, told The Washington Post.
One night in September 2020, Roessler came home and noticed that some jumping spiders she had collected and placed in boxes on her windowsill were hanging upside down from their lines of silk, much like small Christmas tree ornaments.
“I was like, we don’t know what they’re doing, but they’re hanging really neatly, super exposed, not in a silk retreat, so let’s find out and film them throughout the night,” he said. Roessler recalls. . “So that’s what we did.”
What she and her fellow researchers saw amazed them. Using an infrared camera, they observed the young Evarcha arcuata jumping spiders experience limb twitches when suspended upside down. Because spiders had translucent exteriors, Roessler also recorded spiders’ inner “retinal tubes” – a part of the eye that allows arachnids to move their gaze – quivering rapidly during the state of apparent inactivity. This did not happen when the spiders were active.
“These shakes seemed so classic, and they immediately reminded me of a dreaming dog.,” Roessler said.
And it’s possible that spiders dream too, she says.
“Whether that means they visually experience this the same way we experience visual dreams is a whole different story,” Roessler said, thinking spiders can “dream in vibrations.””
Roessler said she and her team weren’t ready to answer those questions. First, they need to prove that spiders actually enter REM sleep. The study cautiously characterizes the behavior as “resembling REM sleep,” since researchers have yet to show that spiders engage in sleep as it is commonly defined by scientists. Roessler said she plans to test those criteria — namely, reduced responsiveness and regulated rest periods — in the future.
But experts in the field, including those who weren’t involved in the study, are excited about its findings.
“I would be really surprised if it wasn’t sleep,” Barrett Klein, an entomologist and sleep biologist at the University of Wisconsin at La Crosse, told the Post. “I would be surprised if they didn’t show reduced responsiveness during these REM-like states.”
Little is known about REM sleep in mammals, birds or other creatures thought to exhibit similar behavior, such as octopuses, experts have said. Klein called REM sleep a “paradox” because an animal’s muscles become largely paralyzed during the sleep phase, while the brain appears to light up as if awake. He also called it a “black box” because it’s unclear why humans and other animals enter the state of REM sleep, and it’s been debated ever since REM sleep was discovered in humans some time ago. about seven decades.
Decoding Dreams: 6 Answers to What Happens in the Sleeping Mind
Some studies suggest that there are “certain psychological or emotional aspects that are specifically orchestrated during REM,” Klein said. “Memory consolidation and a type of learning seem to benefit specifically from REM sleep.”
And some of humans’ most vivid and bizarre dreams take place during REM sleep, said John Lesku, a professor of zoology at La Trobe University in Australia who studies sleep in animals. It is therefore not excluded that animals in which REM-like sleep has been observed – such as dogs, cuttlefish and possibly jumping spiders – can dream, he told The Post, although It’s hard to say for sure because dreams, even in humans, are impossible to prove.
Two people could tell each other they are dreaming, he said. “But strictly speaking, I don’t know if you’re dreaming, and so it becomes even more difficult when you’re talking about non-human animals that you don’t have the ability to ask what they’re doing.”
But if he can assume his cat has dreams, Lesku said, “I’m willing to suggest that maybe the spider does too.”
Before the study published last week, not much attention was paid to whether spiders slept, experts said. “Rather, the hypothesis is that they just take small rests during the day or… whenever they’re active,” Roessler said. “But I don’t think there was such a clear idea if they were actually sleeping for an extended period of time.”
The idea that a jumping spider could enter REM sleep is fascinating to Lisa Taylor, a research scientist at the University of Florida whose research focuses on the behavior of jumping spiders. She said jumping spiders have remarkably complex sensory systems – eight eyes, sensory hairs on their legs, the ability to sense vibrations through surfaces, as well as the senses of smell and sound, and varying degrees of color vision.
“So it’s a really noisy world,” Taylor said, adding that “one of the big challenges animals face is making sense of all this information and deciding one way or another. what to let in, what to deal with and what to do with it all.”
If jumping spiders enter REM sleep, they could consolidate memories or behaviors, because some jumping spiders have sophisticated cognitive abilities and make complicated decisions, Taylor said.
“It’s not little robots that come out and attack everything they see,” she said. “There’s a lot going on in their brains as they decide to attack one thing over another.”
“So if something that happens at night plays a part in that, that’s particularly interesting,” she added.