As with other arthropods, spider's cuticles would block out information about the outside world, except that they are penetrated by many sensors or connections from sensors to the nervous system. In fact spiders and other arthropods have modified their cuticles into elaborate arrays of sensors. Various touch sensors, mostly bristles called setae, respond to different levels of force, from strong contact to very weak air currents. Chemical sensors provide equivalents of taste and smell, often by means of setae. Spider also have in the joints of their limbs slit sensors that detect vibration. In web-building spiders all these mechanical and chemical sensors are more important than the eyes, while the eyes are most important to spiders that hunt actively.
Like most arthropods, spiders lack balance and acceleration sensors and rely on their eyes to tell them which way is up. Arthropods' proprioceptors, sensors that report the force exerted by muscles and the degree of bending in the body and joints, are well understood. On the other hand little is known about what other internal sensors spiders or other arthropods may have.