Minecraft wiki entry for Gathering_resources_on_peaceful_difficulty, associated text: Spider eyes are usually obtained by killing spiders or witches. With these mobs unable to spawn, spider eyes are rather difficult to obtain. The only place they can be found is in the chests of desert temples. Although desert temple chests only have a 29% chance of having spider eyes, desert temples have 4 chests in them, so it is likely that one of them will have some number of spider eyes. However, spider eyes are practically useless on Peaceful difficulty, because they can only be used to be eaten or as a potion ingredient, both of which are impossible in Peaceful.