Endermite

An Endermite is a mob that rarely spawns when an Enderman has been attacked or teleports, or when the player teleports using an Ender Pearl. It was added in snapshot 14w11a.

Appearance
Endermites appear similar to silverfish, but are purple, emit purple ender particles and do not have the thin frills around them that silverfish have.

Behavior
As of 14w11a, endermites are not known to naturally spawn in any biome or dimension, rather they only rarely spawn when endermen are killed (and possibly when they are hurt, although this is not confirmed), and when you throw an ender pearl.

Endermites make the same sounds as silverfish.

Unlike silverfish, which are essentially always moving, endermites do not move for long periods of time when spawned from a spawn egg or using the /summon command.

Endermites are hostile towards the player. Also, endermen are hostile towards endermites, and will easily kill them.

Endermites also cannot seem to enter blocks, like silverfish do.

Trivia

 * Dinnerbone has stated he has an "Ultimate Plan" with endermites that might include the dragon egg. However, he also mentioned he hasn't discussed this idea with the rest of the team yet. (https://twitter.com/Dinnerbone/status/444176255521681408)
 * Endermites are not harmed by water like endermen are, but can still drown if they stay submerged for too long.
 * In normal difficulty, endermites do 1 heart of damage per hit, as opposed to 1/2 heart for a silverfish.