Silverfish are the smallest mob in Minecraft. They appear when the player mines a certain block. The block, named Block Number 97, is available in Creative Mode as a Stone (or Cobblestone) Monster Egg. These only spawn in Extreme Hills Biomes or Extreme Hills Edge biomes. They also appear in Strongholds, where there are Silverfish spawners. Silverfish also drop no reward for killing them aside from experience.
If you mine a block that spawns a Silverfish, it's best to run away until the Silverfish either gets out of the cave or falls over a cliff. When out of the cave, it's safe to kill it. This is because nearby Block 97s will trigger if you attack a Silverfish. Once out of the cave, they are quite vulnerable and weak. Beware when going through Strongholds, as there is a Silverfish spawner next to the End Portal. If you escape a Silverfish without killing it, it may wriggle into a cobblestone/stone/stone brick block and turn it into a Monster Egg. Mossy Cobblestone is safe to break.
Silverfish don't appear to be very smart. However, they do scuttle towards a player if they spot them. This shows that they know how to target something. It is probable that they are predatory, as they feed on decaying matter - and to get decaying matter, something has to die. Some players find them hard to hit due to their small size and fairly rapid movement.
Where they live naturally
- Silverfish and Cave Spiders are the only mobs whose spawning is completely unaffected by the command /gamerule doMobSpawning false. This is because they only spawn from spawners and special blocks, which are not affected by the command.
- Both Silverfish and Endermites, which they are very similar to, suffocate in Soul Sand.