Jumping spiders are fascinating creatures known for their distinctive movement. These small arachnids, belonging to the family Salticidae, comprise over 6,000 described species, making them the largest family of spiders. Unlike many other spiders that rely on webs for capturing prey, jumping spiders actively hunt, and their remarkable ability to leap is central to their predatory lifestyle. They are capable of making agile, targeted jumps. This unique characteristic is a sophisticated method of locomotion that enables them to navigate their environment.
How Jumping Spiders Leap
Jumping spiders do not possess powerful leg muscles in the same manner as many other jumping animals, such as grasshoppers. Instead, their impressive leaps are primarily powered by a unique internal hydraulic system. Spiders lack extensor muscles at two key leg joints: the femur-patella and tibia-metatarsus joints. To extend their legs, they rapidly increase the pressure of their body fluid, known as hemolymph, within these limbs. This sudden surge in hemolymph pressure forces the legs to straighten, propelling the spider into the air.
The cephalothorax, their fused head and thorax, plays a central role in this hydraulic propulsion. Muscles within the cephalothorax contract, decreasing the volume in this area and instantaneously increasing hemolymph flow and pressure into the legs. This internal pressure can reach significant levels, estimated between 9 to 18 pounds per square inch (PSI), roughly equivalent to the pressure of a standard soccer ball. The rapid extension of their legs, particularly the third and fourth pairs, generates the force needed for their ballistic flight.
Before initiating a jump, a jumping spider typically secures a silk dragline to the surface from which it is leaping. This silk tether serves multiple functions. It acts as a mechanical aid for braking, stabilization, and in-air body control. If a jump misses its target or the spider lands precariously, it can quickly climb back up this silk line to its original position. The dragline also contributes to dynamic stability, allowing the spider to adjust its body orientation during the jump for a precise landing.
Why Jumping Spiders Jump
Jumping spiders utilize their unique leaping ability for a variety of purposes, with hunting and evading predators being the most common and significant. Their exceptional vision, considered among the best in the arthropod world, allows them to accurately gauge distances and target their jumps. They are active hunters, and instead of building webs to ensnare prey, they stalk their targets before executing a precise, controlled jump to ambush them. This allows them to capture unsuspecting insects and other spiders, often pouncing from distances of up to 40 times their body length.
Jumping is also an effective defense mechanism for these spiders. When confronted by a threat, their ability to perform quick, agile leaps allows them to rapidly escape danger. They can jump away, often raising their front legs in a defensive posture as a deterrent. Some species can even release silk threads to confuse predators, providing an opportunity to escape.
Beyond hunting and evasion, jumping spiders employ their jumping prowess for other behaviors. They use jumps for efficient navigation across varied terrain, allowing them to traverse gaps or move between surfaces more quickly than crawling. Male jumping spiders also incorporate jumps and elaborate movements into their courtship displays, often involving intricate dances to attract females.