Cave Spider

The Cave Spider is a hostile mob using the same model as the Spider, but with a blue skin and smaller size. They can be more dangerous than the regular spider, but in turn they are much rarer than regular Spiders. Cave Spiders do not spawn naturally; they only come from Spawners found in Abandoned Mine Shafts. Their small size (0.7 x 0.7 x 0.5) allows them to fit through spaces one block wide and just half a block tall including those created by slabs, fence posts and two stair blocks facing each other. Cobwebs don't affect Cave Spiders.

Behavior
Aside from their small size and venom (see below), Cave Spiders inherit most of their behavior from regular Spiders. Cave Spiders behave just like normal Spiders in daylight or light levels of 12 or higher. They can climb walls, jump, 'see' the player through solid blocks, and become neutral in bright light. They are not affected by cobwebs or Splash Potions of Poison. Cave Spiders will climb or leap into an area three blocks high and wait for the player to get close enough to attack. If both cave and regular spiders are attempting to get to the player through a 1x1x1 size opening, the regular spiders crowd the opening and block the path of the smaller cave spider greatly reducing its chance of getting through the opening.

Venom
The most notable feature of the cave spider is its venomous bite. When bitten by a Cave Spider on any difficulty except Easy, the player's health bar turns yellow-green and gradually decreases. The venom inflicts half of a heart of damage about every second and a half, and lasts for 7 seconds on Normal difficulty, or 15 seconds on Hard. Armor does not prevent venom or reduce the damage received from it. Since 1.9 Pre-Release 4 Jeb gave milk the ability to cure the player of the venom. Regardless of the difficulty, venom cannot kill you, but it can drop your health to dangerously low levels.

Milk and Getting Past
Because milk isn't stack-able, using it battle is a waste. The best way to use the milk is after you killed the spiders and lit the spawner. The best way to get past the spawners is to...
 * Block up all the passages to it, dig above and pour lava on the spawner.
 * Dig below and break the spawner
 * Find another way around
 * Drop an Iron Golem in there, if you can.

Other Tips

 * Cave Spiders are faster than normal spiders.
 * Cave Spider spawners are surrounded by Cobwebs, making them difficult to get. Since as mentioned above, Cave Spiders are not slowed by Cobwebs, players can only take extreme caution when passing these areas, unless playing on Easy.
 * They may be able to go through a 1 block gap, but they cannot fit between a fence post and an adjacent block. The most effective method to farm spider eyes is via killing the spiders through the fence gaps; the player can hit them between the gaps with impunity.

Mob farming

 * Because of their small dimensions, building a mob farm from a cave spider spawner would be considerably difficult (unless the player is on the Peaceful setting) and somewhat inefficient to build.
 * If building a mob farm for cave spiders, ensure the roof is not 3 high on the player side wall or they will leap to the roof causing them to get stuck.
 * Cave Spiders do not drop more than one Spider Eye even after being killed by a looting-enchanted weapon.

History
The Cave Spider was first introduced in the Beta 1.8 Pre-release.

SMP servers upgraded from older versions running in peaceful mode may begin spawning cave spiders, though no other monster appears in the world. This is because in older versions setting the Server.properties key  to   would place the server in peaceful mode. As of Beta 1.8, a separate key  must be set to zero to select peaceful difficulty; setting   to   prevents monsters from spawning randomly in dark areas but does not disable spawners. Because the  key defaults to 1 (easy), servers without the key configured at all changed from running in peaceful mode (prior to Beta 1.8) to easy mode (as of Beta 1.8).

As of 1.2 both spiders and cave spiders have gained the ability to climb Ice Blocks.

Trivia

 * The Cave Spider's texture appears to be at a higher-resolution than its normal counterpart - this is because the textures occupy a smaller space.

Bugs

 * Because of the natural tendency of cave spider spawners being created with cobwebs and ceilings, but without walls such as the Moss Stone walls in dungeons, cave spiders can be spawned in the middle of a cavern or a ravine.