If spider promoted on poisoning as sylph on pushing, to just higher tier of self, and spider+++ into base arachnid, I think this would be completely fine. Maybe not even enough to make all spider tiers appealing enough, but I can see trying at least spider+++, and maybe base competes with base sylph for spot ? Anyway, it would be the theme of your original intention, far from too good, and some way to boost spider for at least experimenting with it.