When cast, stone spiders turned up to three pebbles into stone constructs that took the form of monstrous spiders. These constructs could be of any size chosen by the spellcaster, provided they were all of the same size. The constructs were just like natural monstrous spiders, but had enhanced natural armor and were more resistant to damage. They even had a spider's strength-draining poison bite. The stone spiders attacked enemies of the caster as well as they could, unless given other orders while the caster was in earshot.
An alternative use of the stone spiders spell was to grant up to three insectoid vermin of any size or type the effects of a stoneskin spell.
This spell required a cleric to use a divine focus.