Spider Jockey

Spider Jockeys are a combination of two different mobs: Spiders and Skeletons which were introduced in the Seecret Friday Update 8. When a spider is spawned it has a 1% chance of having a skeleton spawn with it, riding on its back. They are treated as separate entities within the game, much like a player riding a pig. Because of this, they have separate health bars, and if one dies the other does not. This "spider jockey" has the ranged arrow attack of a skeleton and the mobility of a spider, making a deadly combination.

When the sun comes up the skeleton bursts into flames while the spider survives. If the spider is killed, the Skeleton will continue to attack and move around.

It is possible for this mob to actually kill itself. Sometimes, the arrows might land on the spider, and other times, the spider might pounce and run the skeleton into his own arrow, making this quite a glitchy mob.

As of Beta 1.2 Spiders are able to climb many blocks in the game. Spider jockeys are also capable of climbing. If the Spider climbs to the ceiling, the Skeleton will start suffocating. A spider's pouncing ability is decreased when it is being ridden. In addition, a Spider Jockey's arrows can shoot through glass and cause damage.

Drops
Alpha: Beta:
 * 0-2 units of string (from Spider)
 * 0-2 arrows (from Skeleton)
 * 0-2 units of string (from Spider)
 * 0-2 arrows (from Skeleton)
 * 0-3 bones (from Skeleton)

These mobs "Spider jockeys" Are not found in 1.5_01 BETA, Well, I have never seen one in my 5 years of minecraft.