With so many Spiderfang in your ranks and 50 points to spare, you might consider a Scuttletide for fun and profit. Either as an area denial or to muck things up right alongside your spiders. ..and you'll STILL have 20 points to spare 😁. A 6" move predatory spell that your (spider) troops are immune to, cast to place anywhere within 6" of a terrain feature, roll 6 dice, 5+ result in mortal wounds against units that end a move or charge within 6" of the Scuttletide...there are worse ways to spend 30 points 😉