Jumping spiders are small to medium in size, stout-bodied and short-legged, with a distinctive eye pattern. The body is rather hairy (pubescent) and frequently brightly colored or iridescent. Some species are antlike in appearance. The jumping spiders forage for their prey in the daytime. They approach prey slowly and, when a short distance away, make a sudden leap onto the unfortunate animal. They are good jumpers and can leap many times their own body length.

Most colorful jumping spider?

You've got to be quick and careful if you want to see a jumping spider capture prey. I've often seen them hunting, but they are so wary that once they catch sight of you, they will usually suspend their activity to keep an eye on you; if you make any sudden moves, they will drop to the ground or hide under a leaf.

Daring Jumping Spider
Phidippus audax

Jumping spiders are easily distinguished from other spiders by their four big eyes on the face and four smaller eyes on top of the head. Around the world there are probably more than 5000 species of jumping spiders. Jumping spiders are charming lil buggers that look up and watch you.  Although a jumping spider can jump more than fifty times its body length, none of its legs has enlarged muscles. The power for jumping comes from a quick contraction of muscles in the front part of the body increasing the blood pressure, which causes the legs to extend rapidly much as the hydraulics in a low-rider car.

Their vision also allows communications by visual means, such as the elaborate courtship dances that males perform. Salticids are perhaps as old and diverse as mammals, though not many humans know their world. Many salticids are colorful, they take on a variety of body forms, and some have disguises, looking like ants and other organisms. The bright colors and elaborate forms of some jumping spider species are involved in courtship.

Phidippus audax is one of the most common jumping spiders in North America. It is commonly called the "bold" or "daring jumping spider." Most casual photographers capture only this species.

Jumping Spider - Phidippus mystaceus
 

Swollen palpi indicative of male spider

This is one of the smallest jumpers I've ever been able to photograph; it is about 3mm long (about 1/8 inch).
Male spiders have an unusual way to get sperm into the females: they use their palpi, the little 'feelers' beside the face. In the females, these palpi are simple and leg-like. Both males and females use them like little hands, to manipulate food and to clean their faces. But adult males have the palpi swollen and more complex (that's one way to tell a male spider: adult and sub adult males have the palpi swollen like boxing gloves).

When the male is ready to mate, he spins a small web and deposits a drop of sperm on it from the underside of his abdomen. He then places the tip of the palp into the sperm, and draws the sperm through the palp's opening into the sperm duct of the palp. There it is stored. The male then goes out in search of females. If he finds one, he performs a courtship dance. If she accepts him, he places his palp against an opening on the underside of her abdomen (her epigynum). He locks it in place by putting a thumb-like projection, the tibial apophysis, into a groove that is usually at the back of her epigynum. The palpus then expands. This happens because the various hard bits of the palp are connected to one another by expandable balloons. When they expand by increasing blood pressure, the hard bits move into position to inject the sperm into the female.*

Eris Species

 
You can see the moveable retinas in this spider's eyes

Jumping spiders have excellent vision, with among the highest acuities in invertebrates. The eight eyes are grouped four on the face (the two big Anterior Median eyes in the middle, and two smaller Anterior Lateral eyes to the side), and four on top of the carapace (two medium-sized eyes toward the back, and two very small eyes in front of them). You can think of the Anterior Median eyes (AME) as acting like our fovea, with high acuity but small field of view, and the remaining six eyes acting like our peripheral vision, with lower resolution but broad field of view.*

Two large Anterior Median Eyes provide acute forward-looking vision

The AME's are long and tubular, which helps their resolution (longer focal length, more magnification) but which means they have a narrow field of view. Since the AME's have a narrow field of view, the spider needs to point them in different directions to see different things. To some extent this is done by moving the carapace, but the eyes can move as well. This is not done by moving the whole 'eyeball', since the lenses of the eyes are actually built into the carapace. Instead the retina moves around, while the lens stays fixed. This retinal movement is accomplished by some small muscles. *

Genus Phidippus: indicative green chelicerae

        
        Phidippus princeps                             Phidippus otiosus

Phidippus princeps - female

Phidippus clarus - male