SpoilerShow
You know, the metal bars on the right side of that room, looking from where you enter it, if you can stand right in front of those bars so that the spider ends up on your left (one square left two squares forward). Result: as long as you stand still the spider will indefinitely rotate not moving away from that position, so if you quickly strife left and launch a prepared projectile and then return to original position the spider has not chance to recover, meaning you can kill it by dodging roughly 2 lightning bolts to set up the situation.
I don't know if this is doable 100% of the time.. but i did it twice in a row.
Edit: ok, does not happen always, however by the off chance that the spider manages to recover from above setup you can keep quickly moving left and right and the spider is as helpless as ever since it will at most move between the two adjacent pressure plates.