If spellcasting is interrupted for any reason, or the arachnids already bear a magical dweomer (for example, they are other creatures polymorphed into spiders), the spell is ruined and the caster is stunned for 1 round.
If this spell is successfully used on any drow (magic resistance fails), the drow is temporarily transformed into a drider under the caster's control. The control is like a charm spell and lasts for 1 round per level of the caster. It is broken instantly if the drider is commanded to do anything contrary to its nature, the known wishes of Lolth, its superiors, or anything clearly fatal to itself. Transformation to and from drider-form takes 1 round, during which time the drider can take no action, and occurs when the spell ends, or upon command of the caster. The affected drow usually (unless Lolth desires otherwise) remembers nothing of its time and actions as a drider.
The material component is a spider of any type small enough to be held in the caster's hand.
Notes: Granted by the drow goddess Lolth.