Spiders are great! It's about time someone built a spider tribal. Just giving a quick look at this deck:
The mana curve is a bit high. You've got a play set of
Arachnus Spinner and a play set of
Spider Spawning. Those are some high cmc, late game cards. I would recommend taking two of each of them out. Even with two copies of each, you your curve is a bit high. It might be helpful to add in some ramp to get to those large creatures quickly. Alternatively, you could put in some ramp and
dredge to fill up your graveyard with creatures in addition to those nyx weavers. That strategy would work nicely, even if you mill your arachnus webs. The ramp would also help you pay for
Graverobber Spider's activated ability late game.