Do spiders dream? A new study suggests it does.

Research ‘in the field’ typically means a trip to the remote Brazilian Amazon for Daniela Rößler, an ecologist at the University of Konstanz. But during the coronavirus lockdowns of 2020, the best she could do was find a patch of bushy grass near her home in Trier, Germany.

Rößler (pronounced RUES-blemish) soon became enchanted by the field’s tiny jumping spiders. After nightfall, some jumping spiders, about the size of her pinky fingernail, retreated into small silk bags called “retreats.” She found others motionless, dangling upside down from a single strand of silk with neatly curled legs—and occasionally moving.

“The way they vibrated reminded me of dogs and cats dreams,” Rößler says.

It wasn’t long before Rößler set up a nursery for baby spiders in her lab to observe their nocturnal dangles. Her new research, published Aug. 8 in Proceedings of the National Academy of Sciencereveals that jumping spiders experience a sleep-like state with rapid eye movements similar to those seen in dreaming humans.

So-called REM sleep, also characterized by muscle relaxation and changes in electrical activity in the brain, is thought to be important in consolidating memory and could play a role in developing important survival skills. Confirming REM-like sleep in jumping spiders could change our understanding of when and how it evolved — so far, REM-like sleep has only been identified in backbone animals (reptiles, birds, fish, and most mammals).

“Spider Intelligence” – and Spider Dreams – “[are] probably completely different from ours in most respects,” said Nate Morehouse, an associate professor at the University of Cincinnati who studies vision and decision-making in jumping spiders and was not involved in the study. “I can’t wait to find out what this new study has given us all to understand them, on their own terms.”

Eye of the Spider

You can’t do a brain scan on a spider like you can in humans or other larger animals, nor can you ask them how they slept, but for baby spiders you can can look inside their heads. In their first ten days of life, jumping spiders, known as salticids, have developed no pigment on the exoskeleton that covers their tiny noggins, a space devoted almost entirely to their eyeballs.

They’re basically “walking retinas,” Morehouse says.

Six smaller eyes provide a 360-degree, monochromatic view of the world that is very sensitive to movement, while the main eyes — the “big, round, cute” eyes — provide high resolution comparable to that of a domestic cat in sharpness, explains. Morehouse out. Although their eyeballs are fixed and cannot rotate in eye sockets like ours, boomerang-shaped retinas move around the back of the main eyes, changing the spider’s field of view.

In her lab, Rößler tried to capture dozing spiders to learn more about their sleeping habits, using a magnifying glass and a night vision camera. She focused on the spiders’ eye and body movements, which provide clues about what’s happening while they’re resting.

She soon found that they experience periods of rapid retinal movement, which increased in duration and frequency throughout the night, lasting about 77 seconds and occurring about every 20 minutes. It was during these REM-like periods that Rößler observed uncoordinated body movements — their abdomens wobbled, their legs curled or not curled.

The spiders’ spinnerets, organs on the tip of their abdomens responsible for making silk, would occasionally “go crazy,” Rößler says. Like the rhythmic foot movements of a sleeping puppy, the spiders seemed to “practice” one of their wakeful behaviors.

Although jumping spiders don’t make webs, “they constantly set small silk anchors wherever they go,” she explains. “They never walk around without leaving a side trail, so in case they jump, they always have a backup line, like a bungee [cord].”

Morehouse says one of the leading theories about REM sleep is that it allows animals to hone essential survival skills.

“Every now and then things happen that I can only explain with the theory that they are having a nightmare,” says Rößler. They will dangle peacefully, legs neatly curled, when suddenly “all legs are extended at once, like aah!”

There were also periods of coordinated movement when the spiders stopped to stretch, adjust the silk line they dangled from, or clean themselves. Judging by the lack of retinal movement, it appears that the spiders briefly woke up to get comfortable before returning to their rest.

To sleep, maybe to dream?

Rößler emphasizes that we have yet to prove that this period of inactivity in spiders can technically be considered sleep. For that, several boxes need to be checked, including showing that the spiders are less arousable, or respond more slowly to stimuli, and require “rebound sleep” if deprived.

From her observations outside, “they really seem to be able to distinguish what is a real disturbance” and what is not, Rößler says.

For example, if there are “vibrations on the vegetation or on the silk, they react immediately,” she says. But when it’s windy, they sway in the wind “and they just don’t care.”

Scientists are convinced that all animals sleep, although what that looks like can vary greatly. Some birds and marine mammals only sleep with half their brains at a time, while hibernating animals can sleep almost continuously for weeks or months. Defining “dreams” is even more challenging, but the periods of REM-like rest imply that the animals have visual dreams.

Jumping at the chance to learn

Other jumping spider researchers described Rößler’s study as incredibly exciting.

“It was a smart idea with relatively simple methods that produced a really profound result,” said Alex Winsor, a doctoral student at the University of Massachusetts Amherst who studies vision in jumping spiders. He and his advisor, Beth Jakob, who has studied jumping spiders for decades, say they’d like to reach out to Rößler with ideas for further research.

“We’re interested in whether they respond to visual stimuli” during this sleep-like state, Jakob said — after all, they don’t have eyelids. Winsor is already developing a system to track the brain activity of jumping spiders, which could provide even more evidence that they dream.

“I use a single tungsten electrode — a very thin wire” placed outside the head to detect electrical activity, Winsor says. The team also plans to combine this with a setup the team previously used to track retinal movements in spiders watching small TVs.

Jumping spiders like evarcha arcuata, the species featured in this study, which are found throughout Eurasia, are the misfits of the arachnid class because they are so visual. Although salticids go to bed (or perhaps wire) in the dark because they can no longer see well enough to hunt, spiders in other families are more likely to be “nappers” with short periods of inactivity during the day and night.

Non-jumping spiders generally have much poorer vision and rely heavily on sensing movement in their webs to sense the world around them, so more research is needed to determine what sleep would look like for them. can see.

“Maybe They’re Dreaming” [in] vibrations,” says Rößler.

Arachnid Ambassadors

With nearly 6,000 species of salticids spread across every continent except Antarctica, it’s almost guaranteed that there’s a jumping spider in your backyard or near you.

Salticides are a “great gateway” for spider-shy, Rößler says — they have the expressive, oversized eyes of a cartoon character, a huge diversity of color patterns, and elaborate courtship dances. There is a thriving community of jumping spiders on TikTok and YouTube — some of them former arachnophobes themselves.

Salticids can make strategic decisions, think ahead, count and – possibly – dream. Morehouse says that people are often both challenged and comforted by learning about jumping spiders’ cognitive abilities — it makes them less strange, but also more worthy of respect or empathy.

‘If they dream, I mean, what can you do? You can’t crush a spider that’s dreaming,” says Rößler.

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