A jumping spider is a visual hunter first. Its two forward-facing anterior median eyes carry a narrow, layered retina that the animal sweeps across a scene using internal muscles. Work published in 2012 showed that these layers let the spider judge distance from how blurred an image is on each layer, a depth cue no other animal is known to use in this way.
The leap that follows is hydraulic in part. Spiders lack extensor muscles at the femur-patella and tibia-metatarsus joints, and a surge of haemolymph pressure straightens the leg. A dragline of silk is paid out on the way, both as a brake and as a line home if the jump misses.
How the work is divided is not settled. Recent measurements indicate that leg muscles supply much of the power, with hydraulic pressure contributing control and speed rather than simply acting as the engine.