From a biological perspective, sleep is a reversible state of reduced sensitivity to external stimuli and decreased physical activity, accompanied by specific neurological and physiological changes. Like humans, most animals on Earth, including spiders, require a state of deep rest to maintain brain function and overall health, as noted by IFLScience.
The differences in brain structure and evolutionary history between humans and arachnids are vast, so it is not surprising that there are some distinctions in our states of slumber. However, what is even more intriguing is that we also share remarkable similarities.
It is known that some spider species can remain motionless for long periods, waiting for prey to become ensnared in their webs. However, they are not actually dozing in this static state; on the contrary, they are tense, like a coiled spring.
According to Richard Zak, a professor of entomology at Washington State University, scientists can indeed determine when a spider enters a state resembling sleep—at that moment, spiders press their bodies into what is known as a "stupor" position.
A 2021 study examining European jumping spiders (Evarcha arcuata) discovered something intriguing. The team observed that spiders typically rest at night, hanging from a single silk thread.
Some researchers prefer to refer to this time spent as a "sleep-like state" or "nocturnal resting behavior" when observed in other animals. However, subsequent studies have also uncovered some fascinating similarities with humans.
It is known that sleep in mammals and birds passes through two main phases:
Spiders have eight eyes, but they lack eyelids entirely, which complicates interspecies comparisons. However, they possess movable retinal tubes that allow them to redirect their gaze, and young spiders have translucent exoskeletons that enable scientists to observe these structures.
In 2022, researchers conducted an experiment and found that jumping spiders enter a state akin to the rapid eye movement phase of sleep. During this state, they also twitch their limbs, somewhat similar to how dogs move their paws when dreaming. As a result, scientists proposed that spiders are likely capable of dreaming, just like humans.