Daniela Roessler and her colleagues glued their cameras to baby jumping spiders overnight to try to find out. The images show what closely resemble sleep cycles: the spiders’ legs fidgeting and their eyes blinking.
Researchers describe this as a kind of
paradoxical sleep which, in humans, is an active phase of sleep closely associated with dreams.
Other animals, including birds and mammals, have REM sleep, but this has never been studied in other species, such as the jumping spider, says Ms Roessler, an evolutionary biologist at the University of Konstanz, Germany.
Their findings were published Monday in the scientific journal Proceedings of the National Academy of Sciences.
The study shows that spiders, during the night, are agitated movements that resemble the twitching of the paws of dogs or cats. It happens in regular cycles, much like sleep cycles in humans.
Several insects similar to spiders have motionless eyes, which complicates the study of their sleep cycles, explained study co-author, evolutionary biologist Paul Shamble of Harvard University.
But these jumping spiders are predators that move their retinas to stalk their prey, he added. In addition, babies have a transparent membrane that opens a window to the inside of their body.
Researchers have yet to determine whether, in fact, spiders sleep while resting, Roessler admitted. This will include testing whether they respond more slowly or not at all to stimuli that would otherwise activate them.
Experts who did not participate in this work are divided on the issue. Some explain that it would be surprising if spiders had REM sleep, as they are so different from humans. Others see it as a great opportunity to study REM sleep and understand a little better what it is for.
REM sleep is
a real black boxsaid an entomologist from the University of Wisconsin at La Crosse, Barrett Klein.