Do Spiders Sleep? What Research on Spider Rest Shows

What counts as sleep?

Scientists cannot ask a spider whether it is asleep, so they look for behavior. An animal is considered to be sleeping if it meets several tests:

• It is still for long periods, usually at a regular time of day.
• It takes a typical resting posture or place.
• It reacts less to disturbance, so it is harder to wake.
• It wakes up quickly when disturbed strongly enough, unlike in a coma or torpor.
• When kept awake, it rests more afterward to make up for lost sleep.

Using these tests, sleep has been found in many animals without backbones. Fruit flies, honeybees and cockroaches all show sleep-like states, and depriving fruit flies of rest harms their learning and memory. Spiders are less studied, but they are now an active topic of research.

How do spiders rest?

Almost all spiders have daily rhythms of activity and rest, but the timing depends on how they live.

The giant house spider, for example, spends much of the day motionless in the funnel retreat at the back of its sheet web and becomes active after dark. Whether its daytime stillness is true sleep has not been studied in detail.

Adult jumping spiders usually spend the night inside small silk shelters, sometimes called pup tents, spun in a crack, under bark or between leaves. The same shelters serve for molting, for guarding eggs and for sitting out bad weather and winter. Because jumping spiders depend on sharp daylight vision, a safe hiding place for the dark hours makes sense: at night they can neither hunt well nor spot predators easily.

Jumping spiders and REM-like sleep

The most striking evidence comes from jumping spiders, which are good subjects because they rely on vision and have movable retinas. Their large front eyes have fixed lenses, but the retinas behind them can move to scan the scene. In newly hatched spiderlings, the body wall is temporarily translucent, so these movements can be filmed from outside.

In a study published in 2022 in PNAS, a team led by Daniela Rößler filmed spiderlings of the European jumping spider Evarcha arcuata at night with infrared cameras. The spiderlings hung upside down from silk threads, motionless, with their legs curled. Every so often they showed bouts of retinal movement together with twitching of the legs and abdomen and stereotyped leg curling. These bouts came at fairly regular intervals, and both their length and the gaps between them increased over the night.

Why REM matters

In mammals and birds, sleep has two main phases. Rapid eye movement (REM) sleep is marked by darting eye movements, muscle twitches and, in humans, vivid dreaming. Non-REM sleep is calmer. Because REM is defined largely by eye movements, it is hard to look for in insects, whose compound eyes cannot move.

Jumping spiders offer a rare chance to look for REM-like sleep in a land invertebrate. The 2022 results looked strikingly like REM: regular bouts of eye movement, twitches and limp limbs. Similar REM-like states have also been described in octopuses and cuttlefish. Because these animals are only distantly related to us, such similarities may show how widespread and possibly ancient REM-like sleep is, or that it evolved several times in animals with complex visual brains.

For more on how these spiders use their eyes when awake, see how well jumping spiders see.

What we still don’t know

The researchers were careful: they described an REM sleep-like state, not proven REM sleep. Important tests remain. Scientists still need to show that resting spiders are harder to wake, that they catch up on rest after being kept awake, and whether the twitching bouts alternate with a deeper, calmer phase as in mammals.

The study also focused on young spiderlings, because adults have dark, opaque bodies that hide the retinas. Whether adult jumping spiders, such as the familiar zebra jumping spider on house walls, show the same pattern is not yet known, and other spider families may rest in very different ways.

Spider sleep myths

Myth: spiders crawl into sleeping people’s mouths. Spiders avoid large, breathing, vibrating animals. The claim that people swallow several spiders a year in their sleep has no scientific basis, as explained in do you swallow spiders in your sleep?

Myth: spiders never rest. Most spiders spend long periods motionless every day. A spider sitting still in a web corner may simply be resting.