By InsightArea Editorial Team
Researchers studying the Australian jumping spider Portia fimbriata have reported evidence of regulated sleep and two distinguishable sleep-like stages, including one with eye movements and muscle twitches. The findings open a window into how sleep may have evolved across animals with very different nervous systems. They do not establish that spiders dream in the human sense.
The study, described by the University of Bonn on October 27, asks a deceptively difficult question: how can researchers tell whether an animal is asleep when its brain and behavior are unlike ours?
Why sleep is more than being still
An animal that remains motionless may be resting, conserving energy or hiding. Sleep is generally studied through a combination of behavioral signs: a characteristic resting state, reduced responsiveness and regulation over time. A stronger case comes from observing how an animal responds when disturbed and whether it compensates after interrupted rest.
The team recorded spiders over several days and nights and used experimental tests rather than relying on a single photograph of an immobile animal. The research focused on one species; it does not show that every spider follows the same pattern.
What makes the REM-like state interesting?
In humans, rapid eye movement sleep is associated with vivid dreaming and characteristic muscle activity. The researchers observed a spider state featuring eye movements and muscle twitches that resembles some of those external signs. The description “REM-like” is deliberately narrower than a claim that the spider experiences human REM sleep in all its biological or subjective details.
Similar behavior can arise through different biological mechanisms. To understand whether the resemblance reflects a shared evolutionary origin or a function that evolved independently, scientists would need comparisons across more species and more evidence about underlying neural activity.
Do the spiders dream?
The observations do not reveal a spider’s subjective experience. In people, researchers can combine physiology with reports from someone awakened from sleep. A spider cannot provide that report. Movement during a sleep-like state is therefore an intriguing clue, not a direct measurement of an imagined scene.
The finding is still valuable without answering the dream question. It suggests that apparently simple nervous systems can support regulated behavioral states that deserve careful comparison with sleep in vertebrates and other animals. Such comparisons may clarify which features of sleep are widespread and which depend on particular kinds of brains.
Why this matters for evolution
Sleep is observed across a wide range of animals, yet researchers are still investigating why it takes the forms it does. A jumping spider offers a different branch of the evolutionary tree from mammals and birds. Studying it can help scientists formulate better questions about the functions and diversity of sleep, while avoiding the assumption that a familiar human label explains every detail.
The next step is not to declare that spiders dream, but to test how robust these states are, how they are regulated, and what their neural mechanisms reveal. As with research on sleep-like states in the waking brain, behavior can reveal a pattern while leaving deeper mechanisms to be investigated.
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