A new scientific study on spiders’ sleep habits found that the creatures may enter an REM dream state, which challenges everything we thought we knew about their cognitive abilities and also offers a unique study into the true purpose of dreaming.
The study specifically targeted 34 Evarcha arcuata jumping spiderlings. In recordings, scientists examined motions in the creatures’ eyes and bodies that are similar to the dream cycles of humans and other vertebrates.
At dusk, the spiders hang from a single silken thread and remain in that position until morning. To the naked eye, they appear to stay motionless as they sleep. But in reality, they have periods of heightened activity. Their eight legs twitch and curl into defensive postures. And while their eyes can’t physically move, the retinal tubes shift rapidly.
What’s even more interesting is that the rentinal movements seem to directly link to the spiderlings’ legs movements. The creatures also stretch or clean themselves shortly after their apparent REM states. And scientists believe that indicates that they briefly awaken after dreaming, just as people do.
While the findings don’t prove that spiders have minds that rival our own, they do open some interesting questions. Furthermore, they could help up understand more about rapid eye movement (REM) sleep in all creatures.
“Finding [the activity] in a system with a much less complex brain, still pretty amazing brain, but less complex than ours, gives us a lot of opportunities to test some of these hypotheses that we have about REM sleep in humans that we can go and test in a system that is much easier to control,” said Daniela Roessler of Harvard University.
Understanding How Spiders Dream May Prove That Animals Use Different Senses For REM-Like Sleep
Until recently, scientists only believed that vertebrate animals dreamed. But in 2019, biologists witnessed cuttlefish enter the dream state. And in 2021, another team witnessed the same state in octopuses.
As Roessler pointed out, reserachers still have years of work before they can difinitively prove that the jumping spiders are sleeping. Though she “personally” belives that the tiny arachnids are “experiencing visual dreams.”
And if she is able to come to the firm conclusion, it will unlock even more questions. For example, the Evarcha arcuata spider has extremely good eyesite, which would give it the ability to record daily visions and experience “movie-like” dreams just as we do. But other spiders have poor eyesite and rely on other senses, like vibrations, to sense the world. So does that mean that they dream in vibrations?
“While sleep is ubiquitous in the animal kingdom,” the researchers wrote, “it remains to be demonstrated whether REM-like sleep is equally universal and how these sleep phases may be expressed in less visual species.”