Spiders that see in colour and jump like telescopes
Jumping spiders (Salticidae) form the largest spider family—nearly 700 genera and about 7,000 species, roughly thirteen percent of all spiders. Their forward-facing principal eyes deliver stereoscopic colour vision used in hunting, courtship, and navigation, while hydraulic legs launch precise leaps without grasshopper-scale muscles.
Eight eyes in a diagnostic pattern sit on a flat, rectangular face: huge movable anterior median eyes for detail, anterior laterals for a wider forward field and looming responses, and rear eyes covering nearly 360 degrees. Principal eyes work like telescopic tubes focusing onto a four-layered retina; green light sharp on the deepest layer and fuzzy above lets them gauge distance by image defocus. Sensitivity often reaches ultraviolet, and some species show UV sexual dimorphism.
Bodies span about one to twenty-five millimetres; Hyllus giganteus is the largest. They breathe with both book lungs and tracheae. Silk becomes draglines for jumps, overnight "pup tents" for moulting and eggs, and winter shelters. Sensory hairs detect airborne sound up to three metres away. Hunting is usually diurnal: swivel the cephalothorax, align the abdomen, stalk, tether silk, then spring.
Jumps rely mainly on third and/or fourth legs, powered by hemolymph pressure rather than bulk muscle. Distances range from a few body lengths to thirty-eight times body length in one Colonus puerperus. Unlike fleas or grasshoppers, salticids aim—vision and rapid processing tailor each leap for gaps, threats, or prey, with the dragline ready to brake or climb back if the landing fails.
Some Portia species plan long detours through bushes to reach prey on distant leaves—behaviour hard to square with a tiny brain. Anasaitis canosa specializes on ants, circling to grab over the head; Phaeacius waits on trunks and lunges downward. Retinal scanning moves inside the carapace, visible through translucent species when attention shifts—an arachnid analogue of saccading eyes.
Source: Jumping spider
