Minecraft wiki entry for Things_not_to_do, associated text: Once the player attacks a silverfish (usually in strongholds), it awakens all other silverfish in the vicinity, meaning the player has many silverfish to deal with. If the player uses a weapon that can kill it in one hit, or if deals damage through indirect means (for example by lighting a fire with flint and steel), the silverfish does not call reinforcements. A diamond sword, or an axe that is stone or better, can kill a silverfish in one hit. Note that the sweeping effect from a sword could damage nearby silverfish without killing.