There has not been a Drider in the city for ages. Once, Lolth used to test her children, and it is said that those who failed were turned into Driders, half-spider, half-drow, with a humanoid upper body attached to a giant spider thorax. But that was so long ago that it has almost assumed legendary status.
Now, WeaponsmasterXarnael has been secretly turned into a Drider, and we don't know if this was done on the GrandTemple's initiative or on Lolth's initiative. Either way, it seems a clear challenge to House Nemalzhi, and especially to Zhe'raen.