Endermite

An Endermite is a mob that occasionally spawns 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 when the player throws an Ender Pearl. Ender Pearls have a 5% chance of spawning an Endermite when used.

Endermites are hostile towards the player. In Normal difficulty, Endermites deal 2 damage per hit, or one heart. Endermites can drown if submerged in water for too long.

Unlike other mobs, Endermites despawn within 2 minutes, regardless of the player's distance from the endermite, unless they are named with a name tag. If they are named, they will never despawn and last until they are killed.

Endermites will take damage if walking on soul sand, due to it sharing its short hitbox with silverfish. Unlike silverfish, a soul sand trap to suffocate endermites is severely inefficient to build, considering their rarity.

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.