Like other jumping spiders, it has vision more acute than a cat and ten times more acute than a dragonfly. The eyes are used to locate prey and rivals, and find and court mates. All spiders have sensors for smell, taste, touch and vibration protruding through their cuticle ("skin").
Jumping spiders can leap up to 50 times their own length by powerfully extending the third or fourth pairs of legs, with the longer forelimbs extended to grasp the prey. P. clarus, a relatively large salticid, takes prey up to the size of an adult earwig. In an experiment, P. claruswas offered as many fruit flies as it could eat, and in four-hour sessions individuals took 17 flies on average – while one took 41.
When P. clarus males compete for females, the winners are those that produce the most vibrations on the surface and those that are largest. Contests between females involve less displaying, and physical fights between females are more likely to end in injury or death. The most successful males choose the largest females, as these produce the most eggs and most quickly. If a female that has mated already then finds a larger male, she will often mate again with the larger male. The average clutch is 135 eggs. Unlike most of the genus Phidippus, P. clarus females die after one brood has left the nest.
P. clarus is parasitized by the Californian wasp Aporinellus completes and by mermithid nematodes. In an experiment in 2006, P. clarus showed promise for controlling the fourlined plant bug, Poecilocapsus lineatus, which severely damages the commercially grown sweet basil.
Jumping spiders have a distinctive rectangular carapace,:51 and that of female Phidippus clarus average 4.05 millimetres (0.159 in) wide, while the carapaces of males average 3.20 millimetres (0.126 in).
Almost all jumping spiders are predators, mostly preying on insects, other spiders, and other non-aquatic arthropods. The most common procedure is sighting the prey, stalking, fastening a silk safety line to the surface, using the two pairs of back legs to jump on the victim, and finally biting the prey. Most jumping spiders walk throughout the day, so that they maximize their chances of a catch.
After capturing the prey, P. clarus settles in one spot and does not move again until it has discarded the undigestible hard remains of the prey. If P. clarus has gone without food for a few days, it eats slowly.:147
P. clarus, which is large by the standards of salticids, takes prey up to the size of an adult earwig. In an experiment, the jumping spider was offered as many fruit flies as it could eat, and in 4-hour sessions specimens took 17 flies on average—while one took 41. When the courtship display of wolf spider Schizocosa ocreata combines visual signals with vibrations, P. clarus responds to its wolf spider prey more quickly than when the wolf spider presents only one of the types of signal.