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 more rare than regular Spiders. Cave Spiders can only be found in Abandoned Mine Shafts. 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 x 1 holes. Their exact size is 0.7 x 0.7 x 0.5.

Venom
The most notable feature of the cave spider is its venomous bite. When bitten by a Cave Spider on any difficulty except Easy, 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 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.

Trivia

 * Cobwebs don't affect Cave Spiders.
 * Cave Spider poison does affect Skeletons, but will not kill them because the venom only brings entities down to half a heart.
 * In SMP, Cave Spider spawners are the only spawners that don't have Pigs in them when they are currently spawning a mob.
 * 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 or lower.
 * Cave Spiders behave just like normal Spiders in daylight.