Familiar Jumpers!

I found this spider on our basement stairs last week.

She is a jumping spider (Salticidae), and a pretty large one. Here is a picture with my thumb to give you a sense of her size. My thumbnail is about a half of an inch (1.3 cm) long.

Jumping spiders don't build webs to trap prey like other spiders. They actively hunt prey and are capable of moving very quickly when necessary. Even though they don't spin webs, they still possess silk glands and they will trail a tiny thread of silk behind them as they hunt. This thread serves as a safety line should they lose their footing when pouncing on their prey.
Two of their eyes are very large and are oriented forward, which gives them better vision for hunting.

The two appendages under her eyes that look like a mustache are called palps. In females, they are mainly used for sensing the environment and manipulating food. Male spiders also use their palps for mating and courtship, so their palps are often larger and more noticeable. One of the clues that this spider is a female was that her palps are not enlarged at the tip. Also, the males of this species have an orange band of hairs underneath their eyes. Jumping spiders are one of the few spider families that possess color vision and the males will often have colorful markings on their faces that serve a purpose in courtship. This species is known as the Familiar Jumper (Platycryptus undatus).
Here is a link to a really great video of some other Familiar Jumpers.