Do Spiders Dream? Two Sleep Stages Found in Jumping Spiders

New experiments suggest that the Australian jumping spider Portia fimbriata has regulated, two-stage sleep, including REM-like eye movements. The results do not prove that spiders dream.

Study: Behavioral evidence for two-stage sleep in spiders · Journal: Proceedings of the National Academy of Sciences · Reported: October 27, 2026

The discovery is about sleep, not confirmed dreams

Researchers at the University of Bonn have reported experimental evidence that the Australian jumping spider Portia fimbriata experiences two distinct sleep stages, including one with movements resembling rapid-eye-movement sleep in humans. The findings, published in the Proceedings of the National Academy of Sciences and reported October 27, expand scientific understanding of sleep in animals with nervous systems very different from our own. The eye movements and muscle twitches are intriguing, but they do not demonstrate that spiders experience dreams. That distinction is essential: scientists can observe behavior, while the subjective content of an animal’s experience is much harder to establish.

Meet Portia fimbriata

Portia fimbriata is a small jumping spider found in Australia and known for its unusual hunting strategies. Members of the genus Portia often prey on other spiders, sometimes manipulating vibrations in webs to lure prey into vulnerable positions. Such behavior has attracted interest from researchers studying learning and decision-making. The animal’s sophisticated hunting does not prove that it dreams, but it makes questions about rest and brain function particularly compelling. Understanding how this spider sleeps may help researchers explore whether complex behavior is associated with distinct forms of sleep across distant branches of the animal kingdom.

Why inactivity is not enough

A spider that remains motionless may be resting, waiting for prey, conserving energy or genuinely asleep. Scientists therefore need stronger criteria than simple stillness. Sleep is often characterized by a reversible reduction in responsiveness, recurring patterns and regulation by the body. One useful sign is sleep rebound: after an animal is deprived of rest, it may compensate by sleeping more later. These criteria allow researchers to distinguish sleep from ordinary inactivity without assuming that an arthropod must behave exactly like a mammal. The Bonn team designed experiments around such behavioral measures.

Watching spiders through the night

The researchers monitored individual Portia fimbriata spiders over multiple days and nights. The animals were housed in dishes measuring 12 centimeters across, and infrared cameras captured behavior without requiring visible nighttime illumination. The recordings documented postures, periods of quiet and episodes involving movements of the eyes and muscles. Repeated observation matters because a single twitch could have many explanations. Patterns across the daily cycle provide stronger evidence of a regulated state. The study relied on careful video analysis rather than invasive brain recordings, which remain difficult in such small animals.

Two sleep stages emerge

The team identified two distinguishable stages during the spiders’ sleep. One involved a comparatively quiet condition, while the other showed characteristic eye movements and muscle twitches. Those movements resemble outward signs associated with REM sleep in humans and some other vertebrates. The similarity raises questions about whether different nervous systems independently developed comparable sleep processes or share ancient biological features. It does not establish that the mechanisms are identical. Behavioral resemblance is a starting point for investigation, not a final account of what happens inside the animal’s nervous system.

How researchers tested responsiveness

To check whether motionless spiders were genuinely asleep, the team used sound stimuli and measured the animals’ responses. An animal in a sleep state may react more slowly or require a stronger disturbance than one that is alert. Designing a reliable stimulus for a spider is not straightforward because its sensory world differs from that of humans. The researchers had to establish conditions under which a response could be measured consistently. This part of the experiment is important because it addresses a common weakness in claims about sleep in unfamiliar animals: behavior that looks restful is not necessarily sleep.

The significance of sleep rebound

Sleep rebound provides evidence that an organism regulates its need for rest. If sleep is interrupted, the animal may subsequently increase sleep duration or intensity. The Bonn researchers used deprivation experiments to examine this response in Portia fimbriata. Such tests help distinguish sleep from a passive period of inactivity imposed by darkness or lack of stimulation. A regulated rebound suggests that the organism maintains an internal balance related to sleep. The result adds weight to the argument that these spiders experience a genuine biological sleep state, even though the study cannot directly reveal the underlying neural circuitry.

What REM-like actually means

In humans, rapid-eye-movement sleep is associated with characteristic eye activity, changes in muscle tone and frequent reports of vivid dreams after awakening. Researchers use the phrase REM-like when another animal shows some outward features but the full physiological correspondence is uncertain. For Portia fimbriata, the observed eye movements and twitches are real behavioral findings. What remains unknown is whether they arise from the same neural processes that produce human REM sleep. Calling the state REM-like preserves that uncertainty and avoids suggesting that a spider’s sleep can be classified exactly as a person’s.

Why dreaming remains an open question

Dreams are subjective experiences. Humans can describe them after waking, but spiders cannot provide comparable reports. Scientists may eventually infer aspects of sleep-related information processing through neural recordings or carefully designed behavioral experiments. Yet even a detailed map of brain activity would not automatically establish what an animal experiences. The current study does not include direct measurements of the spiders’ brain activity. It therefore supports claims about regulated sleep and REM-like behavior, not a definitive answer to whether spiders dream. The question makes an appealing headline, but the evidence deserves more precise language.

An evolutionary puzzle

Sleep is widespread among animals, but its evolutionary origins remain uncertain. If similar sleep stages occur in distantly related species, researchers must ask whether those features were inherited from a remote common ancestor or evolved independently because they solve similar biological problems. Spiders offer a valuable comparison because their nervous systems differ substantially from those of mammals and birds. Discovering structured sleep in Portia fimbriata may help researchers identify which aspects of sleep are fundamental and which are specialized adaptations. Answering that question will require studies across many species rather than one spider alone.

Possible links to learning

Portia spiders’ hunting strategies suggest an ability to adjust behavior based on experience. That raises an interesting possibility: perhaps different sleep stages contribute to memory or learning, as researchers have investigated in other animals. The new study does not demonstrate that a particular sleep stage improves hunting success or consolidates memories. Such a claim would require experiments that connect sleep manipulation with subsequent behavior. Researchers can now design those tests with a stronger understanding of when the spiders are asleep and which stages occur. The discovery is therefore a foundation for future cognitive research.

The limits of behavioral evidence

Without direct neural measurements, scientists cannot determine exactly how the observed stages correspond to electrical activity inside the spiders’ brains. Video analysis also requires careful definitions of what counts as an eye movement, twitch or transition between states. Laboratory conditions may differ from natural environments, where spiders face predators, changing temperatures and irregular light. These limitations do not erase the evidence for regulated sleep. They define what the study can and cannot support. Independent observations and complementary techniques would make the interpretation more robust.

Artificial light could become a research question

The University of Bonn team is interested in whether artificial light at night affects spider sleep. Urban lighting can alter the daily rhythms of many organisms, but its consequences for different arthropods remain poorly understood. Because the new experiments identify recognizable sleep states, researchers have a basis for testing whether light exposure changes their duration or timing. Such work could connect laboratory discoveries with ecological questions. The October findings themselves should not be taken as proof that nighttime lighting has already damaged the sleep of Portia fimbriata populations.

Comparing laboratory and wild spiders

A spider observed in a small laboratory enclosure may sleep differently from one in a natural web or vegetation. In the wild, temperature, hunger, competition and the threat of predation can influence behavior. Researchers hope to compare sleep patterns across environments and species. That comparison is essential for understanding whether the two-stage pattern is typical of Portia fimbriata or dependent on particular conditions. It may also reveal how sleep is balanced against the need to hunt and avoid danger. A controlled experiment is valuable precisely because it isolates variables, but field studies help establish ecological relevance.

What the study changes

The clearest conclusion is that the researchers found experimental evidence for regulated, two-stage sleep in a jumping spider, including a phase with eye movements and muscle twitches. This broadens the range of animals in which complex sleep can be studied and creates opportunities for research into evolution and cognition. It does not show that spiders dream in the human sense, nor does it explain every function of sleep. The value of the discovery lies in replacing a simple assumption about inactive spiders with a testable account of their nightly behavior.