So with the latest patch spiders can climb walls. What can we do to secure our towns/castles/hovels against these new mobile menaces? Does adding a lip to the wall work? Or is there some block they won't climb?
This answer has gone through many, many edits, so I decided to overhaul it. (Minecraft Forums user Thescorpi0on did a number of tests on this.)
Things that will stop spiders:
- A lip extending off of your wall
- Ladders on the top of your wall
Things that won't stop spiders:
- Cacti (it will injure them but they can climb up them)
- Ladders going all the way up your wall (they will start climbing at the bottom all the way up)
In addition to the above methods, I've found that a cactus wall around my tower ends up murdering all the spiders. They climb to the top of the cacti and sit there. They can't get to the tower wall because of the necessary one space gap involved with a cactus wall and proceed to die to the cacti spikes.