​Spiders jump and hunt during the day, sleep and possibly even dream at night, according to a study that found rapid, rhythmic eye movements and behaviors that seem to indicate the existence of sleep stages.

A study conducted by observing the nocturnal behavior of Evarcha arcuata spiders revealed that these invertebrates squirm at night and their eyes move rapidly, as if they are in REM sleep.

In humans, REM sleep is dreaming sleep, and the connection between what you’ve learned during the day and what’s already in the brain appears, it’s a kind of network. This has many advantages, children get a lot of REM sleep, and in this phase the new things loaded into long-term memory are interconnected with the rest of the cortical areas, and so some people say that they had creative ideas in their sleep.

REM comes from “rapid eye movement” because researchers observed the eyeballs moving rapidly from side to side under the eyelids during this stage. In infants, even more than half of sleep is spent in the REM sleep phase, while in adults this indicator is on average 20-25%.

Daniela Ressler of the University of Konstanz in Germany noticed that spiders squirmed and jumped suddenly at night, like dogs or cats do in their sleep. For this study, 34 spiders were photographed overnight.

The studied spiders have six smaller eyes and two larger ones. The study tracked retinal movements in these arachnids and found that there are longer periods during the night when the movements increase in intensity and duration, with an average of 77 seconds of retinal movement every 15 to 20 minutes.

There are still steps to be taken to prove that these spiders are actually sleeping, but Barrett Klein, an entomologist at the University of Wisconsin-La Crosse, says we can go a little further and imagine that spiders really do dream.

“I can imagine a flashback that would allow them to solve a number of problems,” Klein adds. Although the spiders studied are small, they have complex brains for their size and are skilled hunters who make very precise movements, and some studies suggest that they plan their hunting route. These jumping spiders can make what scientists call “strategic decisions.”

Scientists believe that all animals sleep, but the way in which sleep occurs, and especially the weight of the brain that is active during sleep, varies. It is much more difficult to determine what an animal’s dreams mean, but the fact that animals have restless REM periods may mean that they also have visual dreams.

The study was published in the journal PNAS under the title: Regular bouts of retinal movements indicate REM sleep in jumping spiders.

Sources: New York Times, National Geographic, phys.org