How Large Are the Central Nervous Systems of Spiders?

The central nervous system — basically the brain and two nerve cords — of some small spiders can take up about 80 percent of their bodies, overflowing from their body and bulging out into their legs. This leaves only about 20 percent for all the other parts of the spider, including the eyes, stomach, throat and legs. By comparison, humans' brains take up about 2 or 3 percent of their mass, but if humans were built like these spiders, the brain and spinal cord would take up more body mass than the muscles and bones combined.

More facts about spiders and brains:

• Spiders aren't the only ones with proportionally huge brains. Some ants have brains that take up 15 percent of their bodies.


• The relationship between brain size and body size is known as Haller's Rule, which states that the smaller an animal is, the larger proportion of its body the brain will occupy. Haller's Rule also applies to the size of an animal's eyes.


• Spiders have smell-related receptors in some of the hairs on their legs.

Frequently Asked Questions

How large is the central nervous system of a spider compared to its body size?

The central nervous system (CNS) of a spider is relatively large in proportion to its body size. In some spider species, the CNS can occupy up to 80% of the cephalothorax, the fused head and thorax region. This is because spiders require complex neural processing for their predatory lifestyle, including intricate limb coordination and sensory perception.

Do all spiders have the same size central nervous system?

No, the size of a spider's central nervous system can vary among species. Factors such as the spider's size, ecological niche, and sensory requirements influence the CNS size. For instance, web-building spiders may have different CNS configurations compared to hunting spiders, reflecting their distinct behavioral adaptations and sensory demands.

What is the role of the central nervous system in spiders?

The central nervous system in spiders is crucial for controlling movement, processing sensory information, and coordinating complex behaviors such as web construction, hunting, and mating. It integrates signals from the spider's eyes, legs, and other sensory organs to navigate their environment and interact with other organisms effectively.

How does the central nervous system of spiders compare to that of other arthropods?

Spiders, like other arthropods, have a segmented central nervous system. However, spiders tend to have a more centralized nervous system compared to insects, whose CNS is more elongated and segmented. This centralization in spiders supports their sophisticated motor control and sensory processing capabilities necessary for their predatory lifestyle.

Can the size of a spider's central nervous system change during its lifetime?

The size of a spider's central nervous system is generally established during its development and does not significantly change throughout its lifetime. However, as spiders grow through molting, their CNS must also accommodate their larger body size, although the proportional size relative to the body may remain consistent.

Does the complexity of a spider's web correlate with the size of its central nervous system?

There is a correlation between the complexity of a spider's web and the sophistication of its central nervous system. Spiders that weave intricate webs, such as orb-weavers, have central nervous systems that are capable of processing more complex spatial information and motor coordination than spiders that do not construct webs or build simpler structures.