The sense of vision
Jumping spiders have one of the best sense of vision among arthropods, what is essential for hunting, navigation and courtship. With their characteristic oversized principal eyes they can detect even smallest details. The three secondary pairs of eyes are sensitive for motion and they give the jumping spider almost a 360° field of view.
To estimate the distance to the potential prey, jumping spiders are truly masters of calculation. Not only the distance has to be judged correctly, obstacles or wind come also in the equation.
The principle eyes are built like a telescopic tube with a 4-layered retina at it's bottom. The two deepest retina layers are sensitive to green light, but only the deepest receives a sharp focused picture. The layer above will receive an "out of focus" picture. By measuring the amount of fuzziness it's possible to calculate the distance to the object in front of them. Amazing if you consider that their head usually is smaller than the head of a pin.