Spiders Have REM‑like Sleep

A PNAS study finds Australian jumping spiders (Portia fimbriata) exhibit a free‑running circadian rhythm, REM‑like bouts marked by limb and retinal twitching, elevated arousal thresholds during those bouts, and rebound after sleep disruption, based on continuous infrared recording and behavioural startle tests. The work uses lab manipulations and quantitative reaction‑time measures rather than EEG to infer sleep architecture in a tiny invertebrate. — If REM‑like architecture exists in small arthropods it shifts the baseline for theories of sleep evolution and function, affecting neuroscience, animal cognition, and public narratives about what kinds of minds warrant ethical and scientific concern.