Plate Nº 17 · recorded October 30, 2026
Biology & EvolutionReported finding
Bonn researchers report two-stage sleep in jumping spiders
University of Bonn researchers report two sleep stages in Portia jumping spiders, including REM-like eye and muscle movements, based on behavior rather than brain activity.
By James Calloway5 min read970 words
In brief
- Researchers observed two distinct sleep stages in Portia fimbriata over several days and nights.
- The REM-like stage featured eye movements and muscle twitches.
- Each spider was monitored in a plastic dish 12 centimetres in diameter under varied lighting and infrared cameras.
- The team could not measure brain activity, so dreaming remains unconfirmed.
- The University of Bonn report is dated October 27, 2026; the paper appeared in PNAS volume 123, issue 45.
By James Calloway
University of Bonn researchers observed two distinct sleep stages in the Australian jumping spider Portia fimbriata in 2026, including a REM-like phase marked by eye movements and muscle twitches.
That pattern resembles human REM sleep, a phase linked to rapid eye movement, muscle activity and vivid dreaming. Researchers did not record the spiders’ dreams or show that their brains undergo the same changes seen in vertebrates. REM-like is a behavioral description, not a verdict on imagination.
The Bonn team at the Institute of Organismic Biology monitored the spiders over several days and nights. The university called its result the first comprehensive experimental confirmation of “genuine, regulated sleep,” rather than simple inactivity. That is a strong claim by the study’s home institution, so it deserves a boundary. The team had no brain recordings.
A small hunter with unusual behavior
Portia fimbriata grows to roughly the size of a one-euro coin when fully grown. Members of the genus Portia, unlike many spiders that mainly catch insects, specialize in hunting other spiders. They imitate the vibrations of struggling insects trapped in webs, luring web builders toward what seems an easy meal.
Those deceptive strategies suggest unusual learning abilities. That makes the species useful for probing links among sleep, nervous-system function and cognition, though the current experiment did not measure either learning or dreaming.
What the experiments show
Researchers identified two clearly distinguishable stages. During REM-like episodes, the spiders moved their eyes and twitched their muscles. Recordings also captured their sleeping positions and quiet-rest periods, giving the team behavioral patterns they could compare across days.
The team placed individual spiders in plastic dishes measuring 12 centimetres in diameter. It monitored them under different lighting conditions to map daily activity and rest cycles, and through the night with infrared cameras, avoiding visible light.
- Response tests: The researchers played sounds and measured how quickly spiders reacted. A slower response helped distinguish sleep from ordinary stillness.
- Sleep disruption: They interrupted sleep and tested for a response the researchers called “sleep rebound,” meaning extra sleep after lost sleep.
- Long recordings: High-resolution video collected over many days and nights produced large datasets for classifying behavior.
The deprivation test was meant to strengthen the behavioral case, because simple inactivity would not by itself predict recovery through more sleep. Yet the university’s release gives no spider count, timing of sleep interruptions or size of the response, so readers cannot judge its consistency or magnitude from the release alone.
What the evidence can—and cannot—show
Spider sleep presents a practical obstacle: an observer cannot simply ask whether movement has stopped because the animal senses the world differently. The team first had to find a sound that produced a consistent response, then use reaction speed to distinguish sleep from ordinary inactivity.
The central limitation is direct: the researchers could not measure brain activity. Every stage label rests on outward behavior, carefully recorded but without a neural signal that could confirm mammalian-style REM. The movements might reflect a shared ancestral mechanism or an independently evolved one; this study does not resolve that.
Nor did the experiments test whether the animals dream, whether learning improves during a sleep stage, or what the twitches mean. Calling the phase REM-like signals the resemblance without claiming equivalence.
Why the pattern matters
Most sleep research comes from vertebrates—animals with backbones—especially mammals and birds. A comparable two-stage pattern in a spider could show that organized sleep stages extend to an animal with a very different nervous system. Comparisons across species might reveal whether sleep mechanisms are widespread or arose independently.
Behavioral scientists, neuroscientists and researchers in chronobiology—the study of biological rhythms—could use such comparisons to investigate sleep’s evolutionary origins and possible functions. Yet the study identifies a pattern, not its purpose. One species and one set of outward movements cannot establish why sleep evolved or what it does.
The researchers argue for comparisons beyond traditional model animals, including species with unusual adaptations or much simpler nervous systems. Even decades of intensive human sleep research leave basic questions unanswered.
Research still ahead
The Bonn team has several planned studies, not completed results:
- Species comparisons: Researchers will examine how sleep, particularly REM-like sleep, varies among spider species.
- Wild versus laboratory: They plan to compare spiders sleeping in natural environments with those observed in dishes to test how surroundings influence behavior.
- Sleep and cognition: The team wants to study what happens inside the brains of spiders and insects during sleep and whether sleep stages contribute to learning and other mental processes.
- Environmental pressure: Future work will test how climate change and human-driven artificial light at night, abbreviated ALAN, may interfere with sleep in spiders and other arthropods, a group that includes spiders and insects.
What does this change for sleep research?
For researchers, the practical change is a new species outside the mammal family for testing which parts of sleep are ancient, shared and essential. Portia combines complex hunting with observable sleep stages, but the missing neural measurements set a clear next task. The study expands the comparison; it does not yet rewrite what scientists know about human dreaming.
Any claim that spiders dream outruns the evidence. The stronger conclusion is that at least one jumping spider shows organized, experimentally testable sleep, and that possibility now deserves direct neural investigation.
The study
The paper, “Behavioral evidence for two-stage sleep in spiders,” appeared in Proceedings of the National Academy of Sciences, volume 123, issue 45 (2026). Nadja Geiger, Maxim Q. Capelle, Phillip Rosentreter, Marie E. Herberstein, Armin Bahl, Massimo De Agrò, Barrett A. Klein and Daniela C. Rößler authored it.
The University of Bonn released its report on October 27, 2026. The paper’s DOI is 10.1073/pnas.2618030123.
via dx.doi.org (Original)
More from James Calloway
Show full bio
Staff writer covering regulation, policy and their impact on general science news at SciBeat.
267 articles
Nearby plates
- Two Deep-Sea Spider Species Confirmed to Glow With Their Own Blue Light
- REM Sleep Paradox: Brain's Energy Drops Despite Higher Fuel Supply
- Fruit Fly Brains Reveal How a Neural Gate Switches Memory On
- Butterfly Wings Trick Predators With Optical Illusions in Flight
- Wasps Are Hijacking 10-Million-Year-Old Ant Homes in Borneo's Trees