Endermite

An Endermite is a mob that occasionally spawns when an Enderman teleports, or when the player teleports using an Ender Pearl.

Appearance
Endermites are small purple creatures with one red eye and a short, stubby tail. Endermites emit the "portal" particles like other end-related items and mobs.

Behavior
Endermites do not currently spawn naturally in any biome or dimension. Instead they occasionally appear in the place of an Enderman that teleports, or when the player throws an Ender Pearl. Each individual Enderman can only spawn a limited number of Endermites; every time it teleports, the chance of producing one is 15%, minus 1% for each Endermite it has already spawned. Ender Pearls have a 5% chance of spawning an Endermite when used.

Endermites are hostile towards the player. In Normal difficulty, Endermites do 2 damage per hit, as opposed to 1 damage for a silverfish. Endermites are not harmed directly by water like Endermen are, and while they do move freely in water, they cannot swim and will drown if submerged for too long.

Due to some lingering Silverfish mechanics, if left alone, Endermites will try to "burrow" into a block, but, unlike silverfish, said blocks cannot be inhabited by Endermites. Similarly, Endermites make the same, albeit slightly deeper sounds as silverfish. Unlike other mobs, Endermites despawn within 2 minutes, unless they are named with a name tag. If they are named, they will never despawn and last until they are killed.

The Endermite will take damage if walking on Soul Sand, probably because it is less than a block in height yet solid, stopping the mite from breathing.

Trivia

 * Endermites are the smallest mob in Minecraft, after the baby chicken.
 * 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.