Spider Jockey

A spider jockey is the rare appearance of a spider being ridden by a skeleton. A spider jockey possesses the ranged arrow attack of a skeleton plus the vision, agility, melee attack and wall-climbing ability of a spider. The skeleton and spider are treated as separate entities in the game, thus 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). A spider jockey can spawn above and below ground. However, generally, underground skeleton riders die of suffocation, due to the spider scaling walls, causing the skeleton to have its head raised into the ceiling and suffocate.

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. Likewise, 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.

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. However, 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). 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.

Trivia

 * 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.
 * 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. This usually happens when a player chased by a spider jockey enters a structure that is too narrow for the Spider to crawl through.
 * Spider jockeys and chicken jockeys are the only mobs that cannot travel through portals. Instead it will go through the portal without travelling through it.
 * When a spider jockey rides a minecart, the minecart will automatically accelerate.
 * 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.
 * In Creative, it is possible to have only the skeleton attack you, and vice versa (as seen above), due to the fact that they are two different mobs.
 * Sometimes, the spider despawns, and the skeleton remains. However, it is still sitting and cannot be hurt.
 * The skeleton can wear armor, as shown by the picture below.
 * It is possible for the spider to suffocate the skeleton rider while climbing a wall, or when the spider walks through a hole the skeleton cannot fit through.
 * If you're attacked by a spider and skeleton separately you have a higher chance of survival because they aren't a single mob; therefore a spider jockey deals double damage but apart the two mobs can easily be dispatched.
 * If a spider jockey jumps into water, the skeleton will jump off the spider.