Silverfish



Silverfish Are mobs that were added in update 0.9.0. They don't spawn naturally, instead they hide inside of Monster eggs (Stone Bricks that holds a silverfish) and when mined they pop out and attack. If attacked a Silverfish will awaken all other silverfish in a 12*11*21 area. If left alone for long enough, a silverfish will re-enter into any block, and turn it into a monster egg. Silverfish may enter Cobblestone, Stone, or Stone Bricks. Once they do, it becomes Silverfish Stone.

Trivia
Lepisma
 * Silverfish are currently the smallest mobs in all versions of Minecraft (apart from the Endermite).
 * Silverfish can be killed with fire, lava or explosions without the Silverfish turning hostile, preventing them from calling in more allies, so long as the player does not hit them directly.
 * When the difficulty is set at peaceful, breaking a monster egg will spawn a silverfish, but the silverfish would de-spawn instantly.
 * Silverfish will never stop moving unless forced into a one-block hole.
 * In real life, silverfish are small, relatively harmless, wingless arthropods that are often found in dark areas in buildings and the wooden pilings of seaside piers and trees. They are infamous for damaging paper-based products.
 * Real silverfish are very small, no larger than a few inches. During cold temperatures they are known to enter a sort of "hibernation" by expelling most of the water in their body. During this state they greatly resemble small stones or gravel, likely inspiring their Minecraft counterparts.