Invertebrates
Jumping Spider
Salticidae · also called jumping spider, salticid
Jumping spiders are the most relatable of the arachnids. They have big, forward-facing eyes that swivel to look at you, they stalk their prey like cats, they leap with a silk rope clipped on for safety, and the males court females with dances so intricate that some have become internet celebrities.
Overview
The jumping spiders, family Salticidae, are the largest family of spiders, with over 6,000 species on every continent except Antarctica — including salticids found living permanently at 6,700 metres on Mount Everest, among the highest-dwelling animals known. They are mostly small (2–12 mm), compact, and often boldly patterned, and unlike web-building spiders they are active daytime hunters that do not build snares.
Eyes like a cat
A jumping spider’s hunting depends on vision unmatched at its size. The enormous front eyes are built like telephoto lenses, with a movable layered retina that lets the spider scan a scene, judge distance, and see colour with an acuity comparable to a small bird. Four smaller side eyes act as wide-angle motion sensors. Spotting prey, the spider turns to face it, creeps closer in a deliberate stalk, and then pounces.
The jump
Spiders cannot extend their legs with muscle; they do it by hydraulic pressure, pumping body fluid into the limbs. A jumping spider uses a sudden pressure surge to fling itself up to about six body lengths. Every leap begins with a silk dragline tacked to the surface — a safety rope it uses to steady its body angle in flight and to climb back if it misses.
The dance
Male jumping spiders court by display. They wave patterned front legs, vibrate their bodies, and — in Australia’s peacock spiders — raise vivid, iridescent flaps on the abdomen and wave them in a precise, drummed routine while the sharp-eyed female judges. A misjudged display can get the male eaten, so the dance also signals that he is a suitor and not a snack.
Status
Jumping spiders have not been assessed as a group and are, collectively, abundant and secure, though individual narrow-range species — some peacock spiders are known from a single patch of scrub — could be vulnerable to habitat loss.
Jumping Spider: common questions
How good is a jumping spider's eyesight?
For an animal a few millimetres long, extraordinary. A jumping spider has eight eyes, but the huge forward-facing pair are the key — each works like a telephoto lens, with a long focal length and a layered retina the spider can move around behind the lens to scan a scene and judge distance and colour. Within their narrow field these eyes give visual acuity comparable to a pigeon or a small mammal, far beyond any other spider and beyond most insects. The smaller side eyes are motion detectors that cover almost 360 degrees and swivel the spider to point its main eyes at anything that moves.
How do jumping spiders jump so far without leg muscles for it?
Spiders have muscles to flex their legs but not to extend them — they straighten their legs by pumping body fluid (haemolymph) into them under pressure. A jumping spider uses a sudden surge of this internal hydraulic pressure to snap its back legs straight and launch itself, covering many times its body length. Just before it jumps it tacks a silk dragline to the surface; if the leap misses or it is knocked off, it dangles from the line and climbs back up. High-speed video shows they also adjust the dragline tension in flight to control their body angle for landing.
Are jumping spiders dangerous to humans?
No. They are venomous in the sense that they use venom to subdue insect prey, but the venom is medically insignificant to people, the fangs are tiny, and jumping spiders are not aggressive — a cornered one is far more likely to jump away or wave its legs than to bite. Many people find them appealing rather than frightening because they are small, fuzzy, boldly patterned, and visibly attentive — a jumping spider will turn to look at you and track your movements, which few invertebrates do.
Why do jumping spiders dance?
Courtship. Males of many species perform elaborate visual displays for females — raising and waving patterned front legs, vibrating their bodies, and in the peacock spiders of Australia, unfurling brilliantly coloured flaps on the abdomen and semaphoring with them in a precise routine, often accompanied by drumming vibrations sent through the ground. The female, with her excellent colour vision, watches and decides. A male that gets the dance wrong, or courts a female who is not receptive, may be attacked and eaten, so the displays are also a way of signalling "I am a mate, not prey."