The question of whether spiders sleep like humans is complex, reflecting a broader scientific inquiry into the nature of rest across the animal kingdom. While these eight-legged creatures do not experience the same neurological cycles as mammals, they regularly enter periods of pronounced inactivity. Recent observations suggest the line between simple rest and true sleep in some spiders may be blurrier than previously understood. This topic requires examining the specific behavioral and physiological changes spiders undergo when resting.
The Direct Answer: Spiders Do Not Sleep Like Mammals
Spiders do not exhibit the cyclical brain activity that defines sleep in vertebrates, such as the distinct stages of non-REM and REM sleep. True sleep in mammals is characterized by specific changes in brainwave patterns and an elevated threshold for arousal. Spiders lack the complex brain structure required to produce these measurable brainwave changes.
When a spider rests, it enters a state of quiescence, marked by physical stillness and reduced movement. This resting behavior allows for physical recovery and energy conservation. The spider’s metabolism slows down, and its responsiveness to external stimuli decreases, though it does not become entirely unconscious.
During quiescence, spiders often retreat to sheltered locations to avoid predators. Web-building species may settle in a corner of their web, while hunting spiders seek out crevices or leaf litter. This reduced activity meets the behavioral definition of rest but does not satisfy the physiological criteria used to classify true sleep in higher-order animals.
Defining Rest and Torpor in Invertebrates
The behavioral state spiders enter is referred to as quiescence or a “sleep-like state,” distinct from the deep, regulated inactivity of hibernation or torpor. Quiescence is a general term for an animal being still and unresponsive, a common form of rest observed across many invertebrate species. This state involves immobility and a decreased reaction time to stimuli, but the animal can be roused relatively easily.
Torpor, by contrast, is a state of deep inactivity where an animal’s body temperature and metabolic rate drop significantly to conserve energy, often due to cold temperatures or food scarcity. While some arachnids, such as Solifugae, undergo periods of dormancy, the regular daily resting cycles of most spiders are less extreme than metabolic torpor.
The criteria for scientifically defining true sleep include rapid reversibility and a homeostatic need, meaning the animal will become lethargic if deprived of the rest. Spider quiescence fulfills the behavioral criteria of immobility and reduced responsiveness, but without clear evidence of the complex regulatory processes found in vertebrate sleep. The physical signs of spider rest are more about energy management and safety than about complex brain state regulation.
Recent Scientific Evidence: Observing REM-Like States
Recent studies focused on the jumping spider species, Evarcha arcuata, have shifted the conversation about spider rest. Researchers observed these highly visual, diurnal spiders at night using infrared cameras, finding that their resting behavior included distinct, periodic movements. These movements consisted of twitching of the legs and abdomen, and, most notably, internal movements of the retinal tubes.
Jumping spiders possess internal retinal tubes that shift to direct their gaze. Because newly hatched spiderlings have translucent exoskeletons, scientists filmed these retinal shifts occurring in bursts during nightly stillness. These bouts of rapid retinal movement, coupled with limb twitching, occurred in regular intervals and durations.
This pattern strongly resembles the Rapid Eye Movement (REM) sleep stage seen in vertebrates, which is closely associated with dreaming and memory consolidation. The presence of a consistent, cycling active-rest state in a terrestrial invertebrate suggests that some form of internal processing, similar to REM sleep, may be taking place.
Scientists cautiously label this an “REM sleep-like state,” as confirming true sleep would require showing that the spiders suffer ill effects from being deprived of these active rest phases. These observations challenge the traditional view that such complex sleep phases are exclusive to animals with advanced nervous systems.
Activity Patterns: Diurnal vs. Nocturnal Species
The time a spider rests is directly tied to its hunting strategy and lifestyle. Spiders are categorized as either diurnal (active during the day) or nocturnal (active at night). This distinction determines when they engage in quiescence.
Diurnal species, such as jumping spiders (Salticidae), rely on excellent vision to hunt prey in daylight. Since they are most active when the sun is up, their sustained rest occurs after dark. They typically find a sheltered spot and enter their sleep-like state throughout the night.
In contrast, most web-building spiders are nocturnal and are most active under the cover of darkness. Orb-weavers, for example, construct or repair their webs at night to catch insects moving in low light. These species, along with other nocturnal hunters, spend their daytime hours in quiescence, concealed in a retreat or secluded corner.