Minecraft spiders climb walls?

I have the problem that my spiders climb up the walls in my Spider Farm. I built this:

What can I do about it?

Maybe he has a different version or platform

I also built it.

You can't do anything about it. But enough spiders come. The ones that get caught are "dropouts".

I use it. The spiders that climb the walls just drown up there and don't clog the spawns. Very effective.

Um… With me the spiders just stick to the signs!