Do spiders dream? Researchers have detected something like REM (rapid eye movement) sleep — which is associated with dreaming in humans — in jumping spiders. But what does it mean?

Training cameras on 34 spiders, they found that the creatures had brief REM-like spells about every 17 minutes. The eye-darting behavior was specific to these bouts: It didn’t happen at times in the night when the jumping spiders stirred, stretched, readjusted their silk lines or cleaned themselves with a brush of a leg.

Carolyn Wilke, Knowable Magazine, “Do Other Animals Dream?,” Smithsonian Magazine, September 13, 2023. The paper is open access.

But then we learn:

Though the spiders are motionless in the run-up to these REM-like bouts, the team hasn’t yet proved that they are sleeping. But if it turns out that they are—and if what looks like REM really is REM—dreaming is a distinct possibility, Rößler says. She finds it easy to imagine that jumping spiders, as highly visual animals, might benefit from dreams as a way to process information they take in during the day.

Wilke, “Do Other Animals Dream?”

In short, it hasn’t even been established that the spiders are sleeping! In any event, we also learn that REM sleep can mean different things in different life forms, and that it has been observed in birds and cuttlefish but not whales and dolphins. One researcher honestly admits that “ … animals cannot report, and this is the biggest problem that we have in purely scientifically and robustly establishing this.”

Then it might make more sense to ask, what would dreaming actually do for a life form? If spiders did dream, what difference would it make? How would we know? We should perhaps look first at dreaming in animals about which we have some personal knowledge.

What about dogs? According to the American Kennel Club, “What we’ve basically found is that dogs dream doggy things . . . The dream pattern in dogs seems to be very similar to the dream pattern in humans.” And cats? They “dream about things that happen when they’re awake.” Horses? Based on their movements during REM sleep, “there is a chance horses re-enact their experiences during the day.”

We are given to understand that these companion animals dream just like people. But they don’t. Human dreams often involve abstractions, symbols, and alternative world scenarios that both require and enable insight. That thought world is not available to dogs, cats, and horses.

Yes, companion animals are like humans in that they dream about the things they think about — but it matters that the things they think about are much more limited in range.

We would never guess the real state of affairs from some of the comments reported in the Smithsonian Magazine story: “If octopuses and cuttlefish dream, ‘it just kind of blows down the walls of what we think about humanity being so special,’ [animal behaviorist Teresa] Iglesias says.” And from neuroethicist David M. Peña-Guzmán: “We want to think that humans are the only ones who can enact that break from the world.” In the real world, humans are special. The content of our dreams amply demonstrates that fact. Attempts to fudge or misrepresent that fact won’t help research into animal behavior at all and may easily hinder it by sending us on the wrong track.

Interestingly, with birds, the popular advice offered was much more cautious: “It is thought that this kind of dreamlike replay during sleep might aid song learning and memory.” That’s much closer to the level at which we really know things about how other life forms think. It sounds more like science. But it is certainly not as popular as the ground(less) war on human exceptionalism.

You may also wish to read: In what ways are spiders intelligent? The ability to perform simple cognitive functions does not appear to depend on the vertebrate brain as such.