Spider Eggs

Spider eggs are the zygotes of giant spiders, which are sometimes used as a magical component. They appear in Ultima Underworld II

Description
After taking the Avatar into her confidence, the sorceress Altara of Killorn Keep would instruct the hero in crafting a scepter which could destroy the Guardian's ability to draw power from various key points across the planes. Along with a specially potentized black pearl and an amethyst rod, an egg casing from a dread spider was necessary to construct this artifact.

The hero would be able to find nesting spiders in the sewers of Britannia and in the Tomb of Praecor Loth, although disturbing any of their eggs would result in the beasts attacking the Avatar.

Trivia

 * A player-made modification for Exult known as the "Keyring Mod" adds an optional sub-quest to The Black Gate which requires the hero to retrieve two spider eggs in order to create a Gem of Dispelling. Such eggs can be found in a spider nest to the south of the mouth of the Lost River.