Whew - found the rule.  Bites qualify as all three of B, S,<strong>and</strong>P, so they do overcome DR/Slashing<br/><br/>http://www.d20pfsrd.com/bestiary/rules-for-monsters/universal-monster-rules#TOC-Natural-Attacks<br/><br/><br/>Admittedly, I'd say a spider's chelicerae are definitely piercing, but the rules don't... and here, the rules are our friends.  ;)<br/>