I've read through lots of complaints about spider farms, and I solved the problem! what I did was take a island, and dug out a 8x9 and 4 block tall area 6 blocks underground (fill in the caves on your island). Then I added 8 blocks of water in the 8th of the 9 blocks. Then I dug out another 2 block tall hallway on the opposet end of where the water is. I then added open doors along that hallway, to hit the spiders, I then dug out anoter 2 blocks high in a 8x2 pattern in the roof inside of the water stream on the row in front of the doors. I then added open fence gates with water sorce blocks the roof hole. then i added the spawners in the back of the room. Fill in any blocks to the left and right of the spawners, the got out. This is a design where spiders can't escape unless you let them. Happy building!
