As far as i know from previous research across the net, Spiders are said to be co-dom, so they come in both hets (spider) and homo (super spider). But both het and homo has no visual differences unlike the Pastel mutation.
If Spiders are indeed con-dom, then technically, if u breed homo x homo, u get all spiders. You may get hets but you cannot tell the difference.
You are right when you said that spider (het) x spider (het) can still produce normals, as that is the case when you breed hets.
