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Humans do it, and so do dogs and birds and some other animals. And a new study shows that spiders experience periods of rapidly shifting eye movement during sleep—a sleep stage associated with dreaming.

The finding is a game changer in scientists’ understanding of sleep in different animals, said Paul Shaw, a professor of neuroscience at Washington University School of Medicine in St. Louis who wasn’t involved in the new research.

For the study, published Monday in the journal Proceedings of the National Academy of Sciences, researchers examined infrared videos of dozens of young jumping spiders sleeping at night. The tiny spiders, which capture their prey using their acute vision and jumping prowess, sleep upside down hanging by a strand of silk.

The videos showed that the spiders periodically twitched and curled their legs as their so-called retinal tubules—components of their lidless eyes—shifted rapidly to indicate that they were experiencing rapid-eye-movement, or REM, sleep. The periods of REM sleep came every 15 to 20 minutes, with each period lasting about 90 seconds.

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