Minecraft wiki entry for Silverfish, associated text: When idle, silverfish enter a nearby deepslate, stone, cobblestone, stone bricks, mossy stone bricks, cracked stone bricks or chiseled stone bricks block, transforming it into the respective infested block if /gamerule mobGriefing is set to true, as per default. They cannot infest mossy cobblestone, despite being capable of infesting both mossy blocks and cobblestone, and they also cannot infest slab and stairs of these blocks. They are also unable to infest andesite, diorite, granite or smooth stone.