Minecraft wiki entry for Spider, associated text: 1–4 spiders spawn in a 3×3×1 space centered on an opaque block in the Overworld at a light level of 0, except in mushroom fields and deep dark‌[upcoming: 1.19] biomes. The block above the spawning space cannot be a full solid block, including transparent ones such as leaves or glass, but non-full blocks (such as soul sand, slabs) are allowed.[3]