NEW YORK, Aug. 9 (US): It’s a question that keeps some scientists awake at night: Do spiders sleep?
Daniela Rossler and her colleagues trained cameras with jumping spiders at night to find out. The footage showed patterns very similar to sleep cycles: the spiders’ legs twitched and parts of their eyes flashed.
The researchers described this pattern as “a state similar to REM sleep.” In humans, rapid eye movement, or rapid eye movement, is an active phase of sleep when parts of the brain light up with activity and are closely associated with dreaming, the AP reports.
Other animals, including some birds and mammals, have been shown to suffer from REM sleep. Organisms like the jumping spider haven’t received as much attention, so it wasn’t known if they got the same kind of sleep, said Rossler, an evolutionary biologist at the University of Konstanz in Germany.
Their findings were published Monday in the Proceedings of the National Academy of Sciences.
Roessler and her team investigated sleep after discovering spiders hanging at night from silk threads in laboratory containers. She had recently collected some jumping spiders for her study, a common species with a brown, furry body and four pairs of large eyes.
“It was the most bizarre thing I’ve ever seen,” Rossler said of hanging spiders.
The research showed that the spiders’ movements throughout the night are very similar to rapid eye movement in other species, she said — such as dogs or cats that shiver while they sleep. And they occurred in regular cycles, similar to sleep patterns in humans.
Study co-author Paul Shamble, an evolutionary biologist at Harvard University, explained that many spider-like species don’t actually have moving eyes, making it difficult to compare their sleep cycles.
But Shamble said these jumping spiders are predators that move their retina to change their gaze while hunting. In addition, small spiders have a transparent outer layer that provides a clear window on their bodies.
“Sometimes, as a biologist, you get really lucky,” Shamble said.
Rossler said researchers still have to figure out if spiders are technically asleep while they are in these resting states. This includes testing whether they respond more slowly – or not at all – to stimuli that would normally release them.
Creatures such as the hopping spider are very far from humans on the evolutionary tree. Jerry Siegel, a sleep researcher who was not involved in the study, said he doubts spiders can really experience REM sleep.
“There may be animals that are active in quiet states,” said Siegel of the UCLA Sleep Research Center. “But are they REM sleep? It’s hard to imagine that they could be the same.”
But Barrett Klein, an entomologist at the University of Wisconsin-La Crosse who was also not involved in the study, said it was exciting to find REM-like signs in such a distant relative. He said many questions remain about the prevalence of REM sleep and what purpose the species might serve.
Klein said REM sleep is “still very much a black box.”