In my hardcore world, I was in my cave spider farm and I noticed that the cave spiders (when angered) below me by a block (in this case, regular cobblestone) and were still able to hit me and give me the poison effect

The video linked isn't the best since my computer isn't that good with recording so ignore the audio and video problems, but you can roughly see the spiders hitting me through the blocks due to my shield deflecting damage.

I'm not sure if this works with regular spiders, but due to cave spider's size, I highly doubt it does.