Jumping spiders are generally diurnal, active hunters. Their well-developed internal hydraulic system extends their limbs by altering the pressure of their body fluid (hemolymph) within them. This enables the spiders to jump without having large muscular legs like a grasshopper. Most jumping spiders can jump several times the length of their bodies. When a jumping spider is moving from place to place, and especially just before it jumps, it tethers a filament of silk (or ‘dragline’) to whatever it is standing on to protect itself if the jump should fail. Should it fall, for example if the prey shakes it off, it climbs back up the silk tether. Some species, such as Portia, actually let themselves down to attack prey such as a web spider apparently secure in the middle of its web. Like many other spiders that leave practically continuous silk trails, jumping spiders impregnate the silk line with pheromones that play a role in social and reproductive communication, and possibly in navigation.