This tutorial teaches how to farm cave spiders.
Cave spiders can be dangerous enemies - they are shorter than a slab, one block wide, and apply the poison effect to the player. This makes them hard to farm. However, with some skills and care, it is possible. Cave spiders drop the same things that spiders do (string and spider eyes). Despite this, cave spider farms are useful because their spawners are easier to find. While a spider spawner may be tucked away in some dungeon, cave spider spawners can be found in many mineshafts.
Before starting the farm, you will need to find a mineshaft that contains a cave spider spawner. The spawner area can be recognized by a large quantity of cobwebs. The cave spider spawner will be in the center of the cobwebs.
Once a spawner is found, there are a few things that need to be done before starting the farm. First, get rid of all the cobwebs with a sword or shears (sword yields string and shears yield the cobweb item itself), and quickly surround the spawner with torches, so that cave spiders won't be able to spawn. Be careful not to accidentally mine the cave spider spawner, because you will not be able to get it back.
The next thing to do is to make the layout for the spawning area. For the best results, make the spawner room a cuboid, with 4 blocks in between the monster spawner and each wall, and 1 block between the spawner and the ceiling, as well as between the spawner and the floor. You should now have a 9 x 3 x 9 area, with the spawner in the center.
When working with the cave spider spawning area, it is strongly recommended to seal off the area you're working with, so that you are not in danger of mobs other than cave spiders attacking.
Once the area around the cave spider spawner is all set up, you can start building your farm. Most farms have 2 basic components, the collector and the grinder. The collector is the area around the spawner, which collects the cave spiders, and moves them towards the grinder. The grinder is what kills the cave spiders. They are usually killed by either the player or an iron golem, because most sources of damage do not damage cave spiders.
The spawning area in a cave spider farm is generally the same as for other spawner-based traps. However, remember that cave spiders are smaller - they can fit through gaps 1 block wide and 1/2 block tall. Also, remember that they can climb walls.
One way to get the cave spiders to go into the grinder is by pouring water on every block on one side of the spawning area. Then, dig down 1 for every block on the opposite side, place a water source block on each side of the ditch, and place signs over each block in the ditch. Now, all the water should eventually flow to one block. If you want to make sure that the cave spiders don't climb the walls, place water sources all along the top of each wall.
The block where all the water flows into should connect to the grinder room (make another channel if needed). Remember that you can stop the flow of water, but still allow mobs and players to get through with signs.
There are two types of grinders for any type of mob farm: a manual grinder and an automatic grinder. For a manual grinder, the player kills the mobs, and for an automatic, some other source of damage kills the mobs. For cave spiders, a manual grinder is cheaper and more efficient than an automatic, but requires the player to be there to kill the cave spiders.
Because of their size, ability to hold breath underwater, and ability to climb walls, water, fall damage is difficult to make effective on caves spiders. Also, cactus isn't very effective, because cave spiders are small enough to go in between two cacti without taking damage. That said, a cave spider can fall a maximum of 16 blocks before dying. The only ways to kill them automatically are magma blocks and iron golems. The easiest way to make a cave spider farm is to use a manual grinder.
Manual grinders require a hole that is too narrow for cave spiders, but large enough to allow players to attack them easily. One simple way of making one is by placing two fence posts next to a closed door:
One of the few ways to kill cave spiders without the player's aid is by placing iron golems in the collection chamber of the cave spiders. Place hoppers along the floor, all eventually connecting to a double chest. The iron golems will kill the cave spiders, and the loot will fall into the hoppers and go into the chest.
The disadvantage of using this method is that cave spiders will damage the iron golems as well, and eventually the iron golems will be killed. It is recommended to have an iron golem farm before trying to attempt this farm (otherwise, you will go through a lot of iron!). This can be mitigated by having the cave spiders land on magma blocks. You can also repair the iron golem by using iron ingots.
Another way is to make a 9x9 plus 4 air blocks under the spawner and one on it. On the floor put magma, and in the upper corners, water. It will push the spiders in the middle. Under the magma block put minecart hopper, and under it a normal hopper which leads to a chest. The storage is expandable. The only thing you have to do is stay at the level of the spawner, right next to the farm.
Another way is to use flowing water to funnel the cave spiders onto a campfire with a block directly above it. The cave spiders can fit in the half-block gap between the campfire and the block and will take damage from occupying the same block as the campfire, and a hopper can be placed underneath. A soul campfire will deal twice as much damage as a regular one.
Once your grinder, whether it's automatic or manual, is fully functional, go back to the spawner room and get rid of all of the lighting that you put up. This should allow the cave spiders to spawn. If desired, you can decorate any part of the farm that may be in view of a player. Also, if you want to enhance the mechanics of a farm, make a sorter (this will only work if you have hoppers underneath your grinder). This way, the string and spider eyes dropped from the cave spiders will go into separate chests.
Now you have finished your cave spider farm, which will supply you of endless string and spider eyes. However, note that in order for cave spiders to spawn, you must be close to the spawner.
Design by wattles
This design is very simple, but requires player intervention. Once the cave spiders are collected in the grinder, the player can hit them to their death. This design takes advantage of the fact that players can hit in between a closed trapdoor and a half-slab, but cave spiders can't climb through it.
Design by BasketMC
In this design, there are two different modes. In one, the cave spiders take lava damage until down to half of a heart, when water puts the lava out. This allows for players to kill them in one hit. In the other, the cave spiders are killed completely. This design is meant for 3 cave spider spawners, but could easily be modified to 1 or 2.