The Daughters of Atlach-Nacha are huge venomous spiders that are nearly completely black, the only exception being the green and gold streaks on their abdomen. Every one of them started out as human, women chosen to become companions of the Great Old One. Women whom had survived the bite of a lethal spider and now had "the mark of the spider".
His servants coerce or kidnap these women into the Spider God's service. Eventually the women undergo a nightmarish transformation, as they shed their skin and change into a giant spider. After which they join Atlach-Nacha in its lair, helping it weave the great web.