Researchers at the University of Konstanz in Germany have been seeking the answer to the age-old question: Do spiders dream of webbed-up sheep? Or at least, do spiders dream in general? And so far it looks like the answer might be "yes." From Knowable Magazine:
Rößler and her colleagues reported on the retina-swiveling spiders in 2022. Training cameras on 34 spiders, they found that the creatures had brief REM-like spells about every 17 minutes. The eye-darting behavior was specific to these bouts: It didn't happen at times in the night when the jumping spiders stirred, stretched, readjusted their silk lines or cleaned themselves with a brush of a leg.
Though the spiders are motionless in the run-up to these REM-like bouts, the team hasn't yet proved that they are sleeping. But if it turns out that they are — and if what looks like REM really is REM — dreaming is a distinct possibility, Rößler says. She finds it easy to imagine that jumping spiders, as highly visual animals, might benefit from dreams as a way to process information they took in during the day.
Spiders aren't the first animal to (potentially) show signs of heightened brain activity during sleep. Scientists have previously observed similar behaviors in octopuses and cuttlefish, as well as bearded dragons and zebrafish.
Do spiders dream? What about cuttlefish? Bearded dragons? [Carolyn Wilke / Knowable Magazine]