Do Spiders Dream of Juicy Flies?

Jumping spiders, unlike Orb spiders, don't use complex webs to catch their prey. A careful approach followed by a rapid leap, is all that's required. A team of University scientists from Germany, Italy and the US, used infra-red cameras to study jumping spiders during their night-time inactivity periods. Jumping spiders are inactive at night, because their day-time hunting relies on visual cues. Many species of these spiders, showed 'periodic bouts of retinal movement, coupled with limb twitching and stereotyped leg curling'. There are obvious parallels with Rapid Eye Movement (REM) sleep in humans, a condition where people have their most vivid dreams (https://www.theguardian.com/environment/2022/aug/20/spiders-dream-study). This finding does not, of course, mean that jumping spiders dream. Similarities in activities do not always signify the same function. Dreaming in humans is something that has intrigued scientists and the general public for decades. Spiders, however, have neither the complex neural equipment nor the same memory-processing needs as humans. It consequently seems highly improbable that jumping spiders are experiencing anything like REM sleep, when they enter their night-time inactivity periods. Perhaps the movements just reflect the spider maintaining vigilence, to deal with night-time threats? Spiders also get eaten.