Spider Jockey

A spider jockey is the rare appearance of a spider being ridden by a skeleton. In Pocket Editions If Minecraft, Skeletons can be seen Riding Cave Spiders, Same Happens With Wither Skeletons

Spawning
A spider has a 1% chance to spawn with a skeleton rider. This means that a spider spawner, spawn egg, or the command can very rarely spawn a spider jockey. Spiders spawned using spawn eggs in the Nether have a small chance (0.8%) of a wither skeleton spawning on them, creating a wither jockey. However wither jockeys cannot spawn naturally in the Nether. Due to the fact that 20% of all skeletons spawned in the Nether are ordinary skeletons, a skeleton may be on the spider the other 0.2% of the time.

Spider jockeys spawned in narrow enclosures can cause the skeleton rider to die of suffocation, due to the spider scaling the walls.

In the Pocket Edition, spider jockeys can spawn with a cave spider instead of a spider.

Drops
The skeleton and the spider both have separate drops when that part of the spider jockey is killed.

Skeleton
The skeleton part of the jockey may drop 0 to 2 bones, and 0 to 2 arrows. The maximum amount of either drop may be increased by 1 for each level of Looting used, up to a maximum of 5 of each.

Skeletons also have a 8.5% chance each of dropping their bow or any equipped armor that they spawned with. The chance of each can be increased by 1% per level of Looting, up to an 11.5% chance.

If spawned wearing a pumpkin or jack o'lantern and killed using the looting enchantment, there will be a chance equivalent to the level of Looting used to drop the pumpkin, up to a maximum of a 3% chance of a drop.

If killed by a charged creeper, the skeleton will drop a skeleton skull.

The skeleton will also drop 5 experience when killed by the player.

Spider
The spider part of the jockey may drop 0 to 2 string. The maximum amount of string dropped may be increased by 1 for every level of Looting on the weapon, up to a maximum of 5 at Looting III.

If killed by the player, spiders will also have a 33% chance of dropping a spider eye. If killed using a weapon enchanted with Looting, and if the spider eye drop fails, there will be a second chance to drop a spider eye, with a chance of 50% at Looting I, 67% at Looting II, and 75% at Looting III.

The spider will also drop 5 experience when killed by the player.

Behavior
The spider controls the movement, so a spider jockey will wander aimlessly in the day and only pursue the player at night or in dimly lit areas when the spider is hunting. The two creatures attack and take damage individually (i.e. if the spider is killed, the skeleton will continue to attack and move, and vice-versa). If a spider jockey jumps into water, the skeleton will jump off the spider.

The skeleton will turn and fire at the player as soon as it sees them no matter the time of day (although the skeleton will quickly burn in sunlight, leaving the spider unharmed). A spider jockey can attack two different players in SMP - this is caused by one player damaging one half of the spider jockey and not the other. If the skeleton shoots another hostile mob, the mob will focus its attack on the skeleton but not the spider being ridden, even after the skeleton is killed. If the skeleton on the spider jockey is shot by another skeleton, it will jump off and leave the spider to engage the skeleton that shot it.

A spider jockey can kill itself - sometimes the skeleton arrows will injure the spider and other times the spider's pouncing will run the skeleton into its own arrow.

When a spider jockey rides a minecart, the minecart will automatically accelerate.