Also known as the Red-backed Jumping Spider, Phidippus johnsoni is one of the largest and most commonly encountered jumping spiders in western North America.   Males have an all-red abdomen, while females have black and yellow markings on their abdomen.  Salticids are free-roaming hunters.  They do not weave a web to catch prey.  They stalk, then pounce on their prey.  Just before jumping, the spider fastens a safety line to the substrate.  It can leap 10-20 times their body length to capture prey.  Their movement is achieved by rapid changes in hydraulic pressure of the blood.  Muscular contractions force fluids into the hind legs, which cause them to extend extremely quickly. 

In the second photo, her hairy pedipalps partially covering her iridescent blue chelicerae, the spider has her anterior median eyes transfixed in front of her.  

The pedipalps are jointed appendages, much like small legs.  They are used by the spider to sense objects, shape their webs, and to aid in prey capture and feeding.  In male spiders, the pedipalps are also used to deliver sperm during mating. 

Jumping spiders have excellent vision, with among the highest acuities in invertebrates.  The 8 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.  The anterior median eyes provide high acuity but small field of view, while the other six eyes act like our peripheral vision, with lower resolution but broad field of view.  Since all eight eyes are fixed in place and can’t pivot independently from the body like human eyes can, jumping spiders must turn to face whatever they want to see well.  This includes moving their cephalothorax up and down, an endearing behavior.