 Jumping spiders have eight eyes, the two large ones in the centre-and-front position (the anterior-median eyes, also called "principal eyes") providing acute vision and housed in tubes in the head.The other six are secondary eyes, positioned along the sides of the carapace and acting mainly as movement detectors.While the middle pair of secondary eyes in most jumping spiders are small, those of "Phaeacius" and other members of the sub-family Spartaeinae are almost as large as the other secondary eyes.