[Darkwind]

I'd suggest just making the spider walkers (or an 'elite' walker) sacred. If you really want living spiders, though, I'd suggest making them genetically engineered (the spiders, though the humans might be too). Spiders that are stronger, faster smarter--a cool multihero could be a spider that's gained sentience and managed to convince its way into serving you rather than being killed and dissected painfully, not necessarily in that order.

Oh, and if you're only lamenting about how to make their armor thematically, I'd suggest some sort of cybernetic implant in the spiders' heads that creates a force field, from the power of their MIND.