Cave Spider

The Cave Spider is a hostile mob in low light levels and a neutral mob in light levels 10 or above, using the same model as the spider, but with a blue skin color and smaller size. They are more dangerous than the regular Spiders, but they in turn are much rarer than them. Cave Spiders do not spawn naturally; they only spawn from monster spawners found in abandoned mine shafts. Their small size lets them slip through small openings, and their poison can rapidly weaken players.

Behavior
Aside from their small size and venom (see below), Cave Spiders inherit most of their behavior from regular Spiders:
 * They are pacified (made neutral) by bright light—daylight or light levels of 9 or higher. Likewise, subjecting them to darkness will render them permanently hostile.
 * They can climb walls when needed and leap at the player.
 * They are not affected by cobwebs or splash potions of Poison.
 * A cave spider can hold its breath underwater for about 16 seconds (320 world ticks/160 redstone ticks), as with other mobs and the player. It takes about 6 seconds (120 world ticks/60 redstone ticks) to suffocate a cave spider to death.

They have two big differences from regular Spiders: One is the much smaller size of the Cave Spider: They take up only a fraction of a block space, specifically 0.7 x 0.7 x 0.5 of a block. Accordingly, they can fit through spaces one block wide and just half a block tall. This specifically includes those gaps created by slabs, atop fence posts, and by two stair blocks facing each other. Note that if both cave and regular spiders are trying to reach the player through the same 1x1x1 size opening, the regular spiders tend to crowd the opening (which they can't pass), and block the path of the cave spiders.

Venom
The cave spider's other special feature is its poisonous bite. When bitten by a Cave Spider on any difficulty except Easy, the player's health bar turns yellow-green and gradually decreases. The poison 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 protect from venom or reduce the damage received from it, unless the armor has the protection enchantment on it. Milk has the ability to cure the player of the poison. Regardless of the difficulty, poison cannot kill the player, but it can drop the player's health to. If they are suffering from the Weakness potion effect, or the difficulty is on Easy, then they will not inflict poisoning.

Mob farming

 * As noted above, the venom and small size of cave spiders makes farming them quite dangerous. If you must, consider these points:
 * Ensure the roof is greater than 3 blocks high on the player’s side of the wall, or they will leap to the ceiling and get stuck.
 * Cave Spiders do not drop more than one spider eye even after being killed by a looting-enchanted weapon, but the chance of one is increased.
 * Because cave spider spawners are so common, they are quite commonly generated near each other. This can provide you with an extremely efficient XP farm, as two or more spawners can work simultaneously (subject to limits of spawning behavior).
 * The most plausible way to contain them is between a door and a fence pillar, leaving a gap that they can't pass, but which you can attack through. (See the picture in the gallery.) The block arrangement discussed above will also work.

Like most mobs, Cave Spiders will suffocate when you drop sand or gravel onto them. Because of their small size, suffocating requires only one block, making it fairly efficient. Although anvils will instantly kill a Cave Spider, they are fairly expensive to make and will often take damage from falling. Lava is especially useful when dealing with spawners, but will burn any drops and/or experience.

Redstone traps may work, provided the spiders are given no chance to escape. Because of their small size, this may prove difficult.

Though TNT will get rid of spiders and blow up the spawner, both tasks can be accomplished much more easily. TNT should only be considered when unable to use any other method.

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.
 * They have the same size shadow as a normal spider.
 * Many speculations have been made about the possibility of a cave-spider-jockey. This however is impossible without third party tools, as cave spiders do not share an entity ID with spiders, like wither skeletons do with skeletons.
 * Cave spiders are one of the five mobs that give a debuff to the player. The other four being the Wither, the Wither skeleton the Witch, and the Elder Guardian.
 * If cave spiders are allowed to spawn via hacks, they will only spawn if the light level is 7 or below.