This is what an Aphonopelma Sp (meaning not quite sure the exact species). "Flagstaff Orange" looks like. They're a fairly docile, but skittish (afraid of you) spider that lives in Arizona. One of the few that do live in the U.S. they are very pretty as adults - as you can see it has a bald patch on its butt from kicking hairs from either encounters with something it thought was a threat, or from marking around its burrow to deter possible threats. When they molt, they get all fresh hairs.
This spider is obese
- and it is likely a female (as far as what they identified it as, however one cannot be sure without the ventral AND molt methods of sexing).
Hairs not only act as a deterrent in the case of their abdominal hair, but as a sensory organ. Imagine you're covered in a shell - how would you be able to feel outside of it? Hairs. That's why they are covered in them - they can sense air movement, vibrations from sound or thumping on the ground, and also moisture (on their feet). They have excellent senses when it comes to their ability to feel - but eyesight is rudimentary at best for them, with it being blurry. They do have multiple eyes, but mostly for light detection. Although "blind" visually, they can "see" sound, as in where a cricket has just landed. They make Daredevil look like a putz... and spiderman a joke.
They grow really slow, and the females live a long time (past 25 is likely) while males do not live past maturity. Every year when people see the "migrating tarantulas" you are actually watching males on their death march, trying to find females desperately before it is too late and they are eaten, or die from being too old (~90% are eaten). Females seldom leave their burrows except at night for food, and they usually do not go far (mostly waiting for something to walk by). Many males become meals if they do not run fast enough (the faster the male, the more females he can reproduce with).