Jumping spider of the genus Heliophanus flavipes and a pen: Hello, are you sleeping?
Photo: Lino Mirgeler / dpa
Do you know those tiny little spiders that often live in window frames?
Arachnophobics fear their jerky movements and even more their jumping ability, because suddenly the little animals are gone.
And worse than a visible spider is only a spider that is suddenly no longer there - and stimulates the imagination.
Actually, jumping spiders don't do anything.
When you zoom in on them in photos, they have hilariously large eyes.
They don't weave webs, but rather jump on their prey, a bit like cats.
Experts from the University of Konstanz have now taken a closer look at the eight-legged friends and made astonishing observations, as they report in the specialist magazine "Proceedings of the National Academy of Sciences".
"We were in the process of filming the nocturnal behavior of jumping spiders and we noticed something surprising," reports behavioral biologist Daniela Rößler on Twitter.
"At regular intervals, they would curl up their legs and twitch in seemingly uncontrolled movements." This reminded the scientist and her team of sleeping dogs or cats, so she asked herself: "Could this be REM sleep?"
Cats, dogs, octopods - now also mini spiders?
REM stands for "Rapid Eye Movement", which is a sleep phase in which the eyes move quickly and in which dreams are also most intense.
The brain waves show a much faster, more varied pattern than in deep sleep.
In addition, the REM phase is suspected of having a positive influence on creative thinking – at least in humans.
How is it with the animal?
But we do know that cats, dogs and gorillas also have REM sleep phases and move jerkily in their sleep, as if they were reacting to dreams.
Whether they really dream the way people dream cannot be estimated because they can't tell you anything about it.
Other mammals also have REM phases, such as rats, elephants and horses, even octopods and some bird species.
REM phases are unknown in reptiles, amphibians and fish.
And now new in the REM Club: Spiders?
Research with a trick
In order to investigate whether the twitching limbs have something to do with REM, Claudia Rößler had to use a trick.
The Dark Sickle Jumper (Evarcha arcuata) she examined has eyes, even eight of them, but they are immobile.
However, what the spider can move is the retina behind the eyes.
So she can see in three dimensions.
And since baby spiders of the
are transparent in the first week of their life, the movement of the retina can be observed.
And lo and behold: when the spiders rolled their legs up uncontrollably or twitched them, the retinas also moved.
Of course, that's still no proof that spiders actually dream.
The researcher also admits this.
"We need to take a closer look at how widespread REM sleep and REM-like behaviors are in the animal kingdom," Rößler explains on Twitter.
"We can still learn a lot, because even in humans, REM sleep is still a big mystery."
A fundamental question is still open: do the spiders sleep at all when they show the twitching observed by Rößler?
Or are they just in a dormant state, like a snooze?
The scientists also want to investigate this further by nudging the supposedly sleeping animals and observing whether they react differently than awake spiders.