1) The name is okay, but it sounds like the kind of name that other races would call them, not a name that they would give to themselves. If you have thought much about the culture of these people, you may want to cook up an internal name for them. It can be fairly weird & difficult to pronounce, hence why other races would just call them Arachnoids.
2) The fluff mentions fangs, with an implication that they are used offensively, but there is no mentioning of a bite attack or a poison attack. Is this intentional?
3) The vestigial bones for extra legs is a nice touch. Kudos.
4) The obsession with the number eight is a bit hokey, at least to the degree with which it is used. What happens to a ninth family member? I'd tone this down, or find more plausible, less restrictive ways that this preoccupation could manifest.
5) There is no mentioning of alignment, but these creatures don't seem terribly evil. That's a good thing, IMO, but I'd like to get your thoughts on where you see them on the alignment spectrum. CN? TN? CG?
6) I understand the rationale behind the +4 DEX, but the reasoning for CON bonus & the CHA penalty elude me. They are not mentioned as being particularly hardy or especially unpleasant. Perhaps those should be toned down or eliminated, as it kinda clutters the design without contributing much.
7) The other stats seem basically fine, but I'd reduce the LA to +1. The abilities are not really worth more than +1LA, & you want people to want to play this race. Compare to dwarves, whisper gnomes, goliaths, & other trait-heavy races.
8) I'd be interested in seeing a PrC for this race, if for no other reason than to get more insight into their culture. Also, you might want to consider designing a racial paragon class
; they're easy to make, & they provide quite a bit of flavor for any given race. Just a thought.