Text by Guananí Gómez–Van Cortright. Photographs by Jacob Saffarian.
Behold the red-backed jumping spider (Phidippus johnsoni), among the most commonly spotted out of at least 50 jumping-spider species found in the Bay Area—and one of the biggest, being roughly thumbnail-size. These miniature predators can live in habitats from beaches to mountains; find them in open areas or perched on fences on warm, sunny days. In summer, females are guarding eggs: a new generation is arriving.
Fuzzy
Different hairs have different receptors, allowing these spiders to taste and smell their surroundings, pick up on vibrations, and detect subtle air movements. Males’ bright colors have often been sexually selected for by the ladies; this is a female.
Leap of faith
Jumpers don’t spin webs to capture prey. Instead, they use their remarkable vision and powerful legs to pounce, ambushing crickets, flies, dragonflies, and even small frogs. The spiders use their third or fourth pairs of legs to leap 10 to 20 times their body length. (Imagine a six-foot human hopping up onto an eight-story building.) If a spider misses its target, no problem—it’ll catch itself on a silk line and climb back up to try again.
Bite-size
At the tips of their muscular jaws, or chelicerae, are venomous fangs. Using the element of surprise, a jumper leaps onto its prey, flips it (if it’s large or feisty), pins it, and injects paralyzing venom. Jumping-spider venom is not dangerous to humans.
I see you!
You can tell jumping spiders apart from their arachnid kin by their signature big, googly eyes. Unlike most invertebrates, they can focus at high resolution and see about as far as cats can. Two smaller eyes at the sides of their heads scan for peripheral motion. A third pair offers motion detection and distance vision, while a fourth is mostly vestigial.
Mani-pedi
Jumping spiders use fuzzy appendages called pedipalps to detect each other’s silk, store sperm, smell and taste things, and maneuver their food into their mouths. If a pedipalp is damaged, a jumper can regrow it, but the new limb might be shorter or more translucent or have less hair, as seems to have happened with this individual’s left pedipalp. Male spiders have boxing-glove-shaped bulbs at the ends of their pedipalps.
Song and dance
Courtship is an elaborate affair. Males prance and show off their fuzzy colors to attract females’ attention, waving their front legs in complex patterns. They drum their other legs and vibrate internal organs to craft a sultry percussive tune. Researchers are investigating how jumpers manage such complex behavior, given that their brains are about the size of a poppy seed. Male jumping spiders get eaten for their trouble about half the time, though less often among the red-backs.
Silk roads
Like Spider-Man, jumping spiders explore the world in all three dimensions, swinging from silk lines to make hasty escapes or sneak up on prey. When exploring, they exude silk from their spinnerets, the silk-producing organs on their butts, to use as safety lines. At night, they rest in spun hammock-like hideaways called retreats, suspended in the crooks of plant stems.
Egg sac
A female jumping spider, like this red-back, spins a silky sac for her 50 to 100 eggs and attaches it to her retreat. Then she guards it while the eggs develop. Look closely for the tiny, leggy bodies visible in some of the eggs above.
Youngsters
After hatching, often in summer, tiny baby jumping spiders molt eight to 10 times over the next nine months before becoming adults. Spiderlings feed off egg yolk before they leave the nest and learn to hunt for themselves. Jumping spiders usually live for about a year, and males often die younger than females.
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