Do animals dream and if so, what about?

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ONE autumn day in 2020, Daniela Rößler drove home with a car full of jumping spiders. Her lab was closed due to covid-19 regulations, so, after a day in a dry field spent corralling her specimens, Rößler had no option other than to bring them back to her house. When, by chance, she checked on them that night, the spiders were dangling motionless by threads of silk.”I had never seen this before,” says Rößler, a behavioural ecologist at the University of Konstanz in Germany, who soon went back to the field with her colleagues. “We started filming them, just out of curiosity,” she says.

They observed the same behaviour, but only at night. Stranger still, some months later, close monitoring in the lab using a night vision camera revealed not only that the spiders were twitching slightly but also that their eyes were moving. That is similar to what happens when humans dream, which raises the irresistible prospect that spiders could be dreaming too.

Jumping spiders aren’t the only non-human animal in which we have recently found evidence of dream states. We are seeing hints of dreaming, and even nightmares, in species throughout the animal kingdom – from pigeons to octopuses. “If we appreciate the functions that could be connected with dreaming, it totally makes sense for animals to dream,” says Rößler. And yet the question remains: do other animals dream like we do and, if so, what they are dreaming about? Figuring this out isn’t easy but it is worth doing, not least because it might even help us to fathom the purpose of human dreams.…