Deep within the mines they began. Originally, those who mined the earth thought they'd struck odd deposits of metal, but the jagged chunks of metal unfurled themselves and spiders of steel and copper, bronze and silver skittered free when the earth imprisoning them turned to rubble. Fangs penetrated the miners' flesh, injecting poisonous mercury into their blood.
Now they haunt those mines, spinning webs of steel which, if walked into haphazardly, can cause potentially fatal slices and gashes.
To destroy them they must be crushed. Their scrap value makes hunting them worthwile - especially if you find a golden Arachnid!