Death spider turned the target's limb, which needed to be touched by the caster, into a living spider, which then started to eat the host it was attached to.
There were two ways to prevent the victim from getting eaten by the limb-turned-spider. First, cutting the limb off and then burning the spider to death was the mundane way. If done within the first minute after the spell took effect, only one foot or hand was lost. Second, one could resort to magic. A remove curse spell combined with a polymorph spell was a secure way to end it. Other means included the use of dispel magic within the first two minutes, or the use of powerful magic like a limited wish or even stronger spells.
Death spider required somatic and verbal components and an assortment of material components. These were a living spider, a drop of digestive juices of any origin, and a tooth of any origin.
- Mark Middleton et al (November 1996). Wizard's Spell Compendium Volume One. (TSR, Inc), p. 219. ISBN 978-0786904365.