Cave Spider

The Cave Spider is a hostile mob that was introduced in Minecraft Beta 1.8. It is a Spider with a blue re-textured skin and is more dangerous than the regular spider, but in turn they are much rarer than regular Spiders. Cave Spiders can only be found in Abandoned Mine Shafts, introduced in Beta 1.8. Cave Spiders are also smaller than regular spiders, presumably so that they can fit through the mine shafts that they spawn in, including 1 x 1 holes. Their exact size is 0.7x0.7x0.5.

Venom
The most notable feature of the cave spider is its venomous bite. When bitten by a cave spider on any difficulty except easy, your 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 5 seconds. Armor does not affect venom; neither the conditions under which you will receive venom, nor the damage received from it. There is currently no known cure for the venom, but Jeb is considering using milk as the cure. Regardless of the difficulty, venom cannot kill you, but it can drop your health to dangerously low levels. Cave spiders do not poison the player on easy mode.

Trivia

 * It was originally going to be called a "tree spider" according to Jeb, but that wouldn't make any sense due to it spawning in mine shafts.
 * In the Beta 1.8 preview, Cave Spiders were called "Poison Spiders"
 * Cobwebs don't affect Cave Spiders.
 * When exposed to sunlight, Cave Spiders do not become passive or burn, they stay hostile regardless.
 * Torching a Cave Spider monster spawner sometimes does not prevent it from spawning spiders.
 * The original, full-sized spider was originally planned to be venomous, but was no longer venomous in the full release of 1.8.
 * Cobwebs seem to spawn near the spawners in a way to 'protect' the spiders by taking up small hallways in mineshafts. However, this may just be a coincidence.