Jumping spiders have joined an elite group of animals known to experience a phase of sleep associated with dreaming in humans.
Rapid eye movement (REM) sleep was known only among vertebrates and octopus until biologists led by Daniela Rößler at Germany’s University of Konstanz quite literally peered into the heads of sleeping baby jumping spiders.
Most invertebrates have immovable eyes, making REM sleep tricky to investigate. But jumping spiders can direct their gaze by moving their retinas, which can be seen through the temporarily translucent exoskeletons of spiderlings in the first few days after hatching.
The biologists report in Proceedings of the National Academy of Sciences that bursts of eye movement are accompanied by limb activity and muscle twitches, which are also seen in vertebrates. In humans, REM sleep is also associated with dreaming.
Rößler now plans to investigate whether the spiders’ brain activity is heightened during bouts of REM. But she is cautious about this line of thought: “It is an enormous step to be wondering about dreams. I think this is amplified by our human bias and our own experience and imagining that ‘dreaming’ would look or feel the same in other animals. Animals experience the world differently, so a ‘dream’ is likely very different.”
Main image: jumping spider (Evarcha arcuata). © ljphoto7/Getty