A jumping spider kept awake overnight made up for it the next night with extra sleep, and its slumber came in two clearly different stages, according to a new study in the Proceedings of the National Academy of Sciences. Researchers at the University of Bonn in Germany say the work on the Australian spider Portia fimbriata is the first comprehensive behavioral confirmation of sleep in a spider, ScienceDaily reported from the university's release.

The finding matters because it meets the standard scientists use to separate true sleep from simple rest. Sleeping animals respond more slowly to disturbances, and they try to recover sleep they lose. Portia did both — placing spiders alongside mammals, birds, fish, and insects in showing regulated sleep.

That raises a practical question for wildlife. If spiders need structured sleep, then the bright nights spreading across cities and suburbs could affect animals that control insect pests in backyards and farm fields. The Bonn team says that is its next line of research.

A Clever Hunter That Sleeps Upside Down

Portia fimbriata is a small jumping spider, roughly the size of a coin, known for hunting other spiders with unusually flexible tactics. Study author Nadja Geiger told ABC News Australia that the species is active by day, relies heavily on vision, and has a distinctive night posture, hanging upside down in a small web.

The team housed spiders in small plastic dishes and filmed them in high resolution over several days and nights, using infrared cameras after dark, according to the University of Bonn release. The spiders showed a quiet stage, in which they groomed and then slowly drooped, and a REM-like stage marked by eye movements, leg curls, and twitching.

To test whether these states were real sleep, the researchers played a loud sound while spiders were awake, in the quiet stage and in the REM-like stage. Reactions slowed in both sleep stages, with the strongest delay during REM-like sleep, and some spiders did not respond at all. When sleep was disrupted, the spiders showed a sleep rebound, recovering rest they had lost.

From Twitching Spiderlings to Measured Sleep Debt

The new work builds on a 2022 study led by the same Bonn researcher, behavioral ecologist Daniela Rößler, that recorded REM-like retinal movements in sleeping spiderlings of a different species, Evarcha arcuata. That earlier PNAS paper suggested spiders might have a REM-like state but did not test the hallmarks of regulated sleep. Nature World News covered that research in its 2022 report on whether spiders dream.

Thomas White, an entomologist at the University of Sydney who was not involved in the study, told ABC News Australia, "This paper is far and away the most complete behavioural case for sleep in any arachnid." White noted that people readily recognize twitching sleep in pet dogs, and that this study goes further by mapping several separate features of sleep in an animal very distant from vertebrates.

Rößler told ABC that comparing sleep across very different animals can help reveal which features of sleep are ancient. Spiders and mammals last shared an ancestor hundreds of millions of years ago, so finding a similar two-stage pattern in both suggests that structured sleep may serve basic biological needs.

Dreaming Remains an Open Question

The study does not show that spiders dream — the university's own summary states plainly that identifying REM-like movements "does not establish whether spiders dream." In people, dreaming is reported verbally and linked to specific brain activity during REM sleep, and neither kind of evidence is possible here.

The researchers also did not record brain activity, so all conclusions rest on behavior. That is a key limit. Without measurements from the spider's nervous system, scientists cannot say whether the REM-like stage involves the same kind of brain processes seen in mammals or birds, and the team noted it had to guard against overinterpreting the twitches.

The findings come from one species studied in a laboratory, so they may not apply to all spiders, including web-building species that hunt by touch rather than sight. Several detailed figures reported elsewhere, including sample sizes and the exact method used to keep spiders awake, should be checked against the full paper, which was published the week of Oct. 26.

Night Lighting as the Next Test

The Bonn team plans to study how human influences affect spider sleep, particularly artificial light at night. Rößler told ABC the next phase will include fieldwork in northern Queensland and Western Australia, looking at artificial lighting and habitat disturbance.

Light pollution is already known to disrupt insects, birds and other night-sensitive wildlife. Jumping spiders are daytime hunters, so a brighter night could, in principle, cut into the quiet hours they use for sleep, but no study has yet measured that effect. Any link remains a hypothesis until the field research is done.

For readers, the practical takeaways are modest. Backyard spiders that hang motionless at night may be asleep, not dead, and they play a useful role in controlling insects. Homeowners who want to reduce their effect on nighttime wildlife can use shielded, downward-facing outdoor lights or motion sensors, a step that wildlife agencies already recommend for birds and insects.

The bottom line: a cunning Australian jumping spider shows the two key signs of true sleep and two distinct stages, including a REM-like phase it works to recover. Whether spiders dream is still unknown, and the next question is whether artificial light at night interferes with that rest.

What Readers Want to Know

What did the new spider sleep study find? Portia fimbriata jumping spiders responded more slowly to sound while asleep and slept extra after their sleep was disrupted, two hallmarks of true sleep.

Do spiders really have REM sleep? They show a REM-like stage with eye movements and twitching. Brain activity was not measured, so it is not confirmed to match REM in mammals.

Do spiders dream? Unknown. The researchers say REM-like movements do not establish whether spiders dream.

Which spider was studied? Portia fimbriata, a small Australian jumping spider that hunts other spiders and sleeps hanging upside down in a small web.

Could outdoor lighting affect spider sleep? Possibly, but it has not been tested. Artificial light at night is the team's next research focus.

Are sleeping spiders dangerous? No. A motionless spider at night may simply be asleep, and most backyard spiders help control insects.