Endermite

Endermites are the second smallest mobs in Minecraft.

Spawning
Using an ender pearl has a 5% chance of spawning an endermite.

Drops
Endermites drop 3 experience when killed by a player or tamed wolf.

Behavior
Endermites will attack players within 16 blocks of them. They have the ability to call other endermites in the area upon being hit, allowing them to see the player through walls.

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 unless they are killed.

Endermites will take damage if walking on soul sand, due to its small hitbox.

Endermen
Endermen will attempt to kill endermites, provided they were spawned from ender pearls and there is no nearby player in Survival or Adventure mode. If the player is close enough to an endermite, enderman focus on the player instead of the endermite.

Video
Note: This video states that endermites can spawn when endermen teleport; this is outdated, as this can no longer occur as of 14w28a.