Jumping spiders (family Salticidae) are small, highly active arachnids known for their keen eyesight and diurnal habits. Unlike many spiders that rely on silk webs, these are agile predators that actively stalk and pounce on their targets. A common behavior is the rhythmic waving of their first pair of legs or their pedipalps. This distinctive motion is a complex form of visual communication, conveying important messages to rivals, potential mates, and even predators.
Courtship and Mating Displays
The most elaborate reason for the waving behavior is the male’s specialized courtship ritual. Males perform intricate, species-specific dances to attract a female and prove their fitness. For example, males of the Habronattus genus use the waving motion to showcase bright coloration on their legs and bodies.
This complex performance involves raising legs in specific patterns, vibrating the body, and displaying colorful ornaments, serving as a direct signal of genetic quality. The female is typically larger and capable of predatory behavior, so the male must convince her he is a suitable mate and not a meal.
The male often supplements the visual wave display with substrate-borne vibrations, sending a seismic song through the surface they stand on. The male’s persistence and precision in his routine are a test, as the female may only offer fleeting attention or even turn away. This ritualized communication prevents the male from being mistaken for prey. Only males who successfully execute the precise combination of visual movement and vibration are likely to be accepted.
Territorial and Defensive Signaling
Beyond attracting a partner, the waving of the legs and pedipalps is a primary method for communicating with other spiders, especially in territorial disputes. When two males encounter each other, they engage in ritualized aggressive displays to establish dominance without physical fighting. They raise and spread their front legs and pedipalps in a threat posture, making themselves appear larger and more formidable.
This visual standoff, known as a lateral display, allows one male to assess the size and determination of the other before a conflict escalates. If one spider perceives the other’s display as superior, it usually retreats, conserving energy and avoiding injury.
Batesian Mimicry
In some genera, such as Myrmarachne, the leg-waving behavior is a defensive strategy known as Batesian mimicry. These spiders are myrmecomorphs, meaning they resemble ants, which are generally avoided by many predators. The spider enhances this illusion by raising and waving its slender first pair of legs, making them look exactly like ant antennae.
This behavioral mimicry is so convincing that the spider can momentarily pause its movement, lift the legs, and appear to be an ant actively sensing its surroundings. This highly specific waving action successfully deters visually-oriented predators.
The Visual World of the Jumping Spider
The effectiveness of these intricate waving displays relies entirely on the jumping spider’s sophisticated visual system. Jumping spiders possess eight eyes, but the pair of large, forward-facing principal eyes provides exceptional vision. These anterior median eyes function like tiny, high-resolution telephoto lenses.
This specialized visual apparatus grants them the highest visual acuity of any arthropod of comparable size. The clarity and detail they perceive allow them to detect the subtle, species-specific patterns of the waving legs and the male’s coloration. Spiders can also perceive a broader spectrum of colors, which is essential for decoding the complex visual signals used in courtship.
The remaining six eyes function as motion detectors, providing a nearly 360-degree view of their surroundings. Once movement is detected by these secondary eyes, the spider quickly turns its body to bring the object into the sharp focus of the principal eyes.