They appeared as female drow of astounding and unblemished beauty with eight spindly arachnid legs protruding from their sides, keeping them from touching the floor. The wizard Pharaun noted that their beauty was transfixing, to the point that he thought the first one he saw was Lolth herself.
They could also hang upside down from the ceiling, just like a spider could.
Even among drow priestesses, they were a myth, and others didn't even know they existed. They acted as handmaidens (presumably along with the yochlols) and as midwives and guardians. Their existence was prophesied, and when the Silence of Lolth came to an end, they came into existence. They were seen guarding the gate from the ruined temple of Lolth in the Abyss to the new Demonweb Pits.
Although they are noted to be different from driders because of their divine beauty, it is unclear if the lower half of their bodies was that of a spider, like a drider, or if they had normal humanoid bodies except for the arachnid legs protruding from their sides and backs.
Magical spiders: Bloodsilk spider • Electric spider • Glass spider • Gaze spider • Goblin spider • Pet of Kalistes • Spellgaunt • Steeder
Planar spiders: Demonweb terror • Fire spider • Myrlochar • Phase spider • Tomb spider • Vortex spider
Constructs: Arachnar • Bone spider • Jade spider • Retriever • Spiderwalker • Stone spider
Creations of Lolth: Abyssal widow • Chwidencha • Drider (Vampire) • Shunned
Outsiders: Bebilith • Darkweaver • Greelox • Inferno spider • Yochlol
Humanoids: Aranea • Chitine • Choldrith • Ettercap • Werespider
Miscellaneous: Kitthix • Neogi • Rhylfang • Susurrus
Undead spiders: Wraith spider