Although they normally move unobtrusively and fairly slowly, most species are capable of very agile jumps, notably when hunting, but sometimes in response to sudden threats or crossing long gaps.

Their front four legs generally are larger than the hind four, but not as dramatically so as those of the crab spiders, nor are they held in the outstretched-arms attitude characteristic of the Thomisidae.

The jumping spiders, unlike the other families, have faces that are roughly rectangular surfaces perpendicular to their direction of motion.

[3][5] The largest is Hyllus giganteus,[5] while other genera with relatively large species include Phidippus, Philaeus and Plexippus.

[6] In addition to using their silk for safety lines while jumping, they also build silken "pup tents", where they take shelter from bad weather and sleep at night.

[10] While unable to form images, the reduced pair of eyes is thought to have a role similar to that of insect ocelli by receiving light from the sky.

[13] Even with all the other pairs covered, jumping spiders in a study could still detect, stalk, and attack flies, using their ALEs only, which are also sufficiently widely spaced to provide stereoscopic vision.

[17] As the eyes are too close together to allow depth perception, and the animals do not make use of motion parallax, they have instead evolved a method called image defocus.

The incoming green light is only focused on the deepest layer, while the other one receives defocused or fuzzy images.

By measuring the amount of defocus from the fuzzy layer, calculating the distance to the objects in front of them is possible.

[17] Some species (such as Cosmophasis umbratica) are highly dimorphic in the UV spectrum, suggesting a role in sexual signaling.

The anterior median eyes have high resolution (11 min visual angle),[22] but the field of vision is narrow, from 2 to 5°.

As the lens is attached to the carapace, the eye's scanning movements are restricted to its retina through a complicated pattern of translations and rotations.

Movement of the retina in jumping spiders is analogous to the way many vertebrates, such as primates, move their entire eyes to focus images of interest onto their fovea centralis.

[25] Jumping spiders' well-developed internal hydraulic system extends their limbs by altering the pressure of their body fluid (hemolymph) within them.

When it detects potential prey, a jumping spider typically begins orienting itself by swiveling its cephalothorax to bring the anterior median eyes to bear.

After that, it might spend some time inspecting the object of its attention and determining whether a camouflaged or doubtful item of prey is promising, before it starts to stalk slowly forward.

Members of the genus Phaeacius take that strategy to extremes; they sit on a tree trunk, facing downwards and rarely do any stalking, but simply lunge down on any prey items that pass close before them.

In their review of the ethology of the Salticidae, Richman and Jackson speculate on whether such web building is a relic of the evolution of this family from web-building ancestors.

Having made contact with the prey, hunting Salticidae administer a bite to inject rapid-acting venom that gives the victim little time to react.

[33] In this respect, they resemble the Mimetidae and Thomisidae, families that ambush prey that often are larger than the predator, and they do so without securing the victim with silk; they accordingly must immobilise it immediately and their venom is adapted accordingly.

More specifically, the jumping spiders displayed a significant amount of action occurring in their retinal tubes and uncoordinated twitches/leg curls under this state.

Given that the jumping spiders were observed from 7PM to 7AM, the researchers realized that these actions were not present while they stretched or readjusted their silk webs outside of this time frame.

The female of the Southeast Asian species Toxeus magnus feeds its offspring with a milky, nutritious fluid for the first 40 days of their lives.

[36] Jumping spiders conduct complex, visual courtship displays using movements and physical bodily attributes.

In addition to displaying colors, jumping spiders perform complex sliding, vibrational, or zigzag movements to attract females.

Some examples appear to be provided by patterns on the wings of some tephritid flies,[50][51] the nymph of a fulgorid[52] and possibly some moths.

The oldest fossils are from Baltic amber dating to the Eocene epoch, specifically, 54 to 42 million years ago.