Silverfish are small, insect like mobs, which have silver skin and two black eyes.
Silverfish don’t spawn naturally, but appear from Monster Eggs which are only found in strongholds and sometimes randomly underground in extreme hills biomes. The blocks they spawn form look identical to normal blocks but when that block is mined or broken a silverfish pops out and attacks the nearest player.
When spawning from monster spawners, the block, they can only spawn in light level 11 or lower, except when on top of stone, where they can spawn at any light level. They also can’t spawn within a 5 block distance of any player. These rules only apply when spawning a silverfish from a monster spawner and not from a Silverfish block.
The safest way to fight silverfish is by standing on top of a 2 block high pillar, which will stop the silverfish from reaching a player. The player then can then kill the angered fish by using non direct attacks such as dumping a bucket of lava or dropping gravel on top of the silverfish. Non-direct attacks will not anger other silverfish.
Using splash potions of poison can be described the worst way of fighting silverfish as each damage they take from the poison will waken other silverfish in that area, immediately gathering a large swarm of silverfish. This can, however, quicken the process of showing which blocks contain silverfish if the player is prepared to take on a large amount at once.
If a silverfish is killed in one hit, it will not gather other silverfish so a diamond sword is best when in combat with silverfish. Just remember that when a silverfish re-enters a block, they are cured of any effects and restore any lost health.
As you do not know when you will be attacked by silverfish, keep your mines large and wide to prevent being boxed in with one.