The Traitor King achievement: "Kill 40 Swarm Scarabs within 30 seconds".
After a few attempts we just barely got the achievement -- not one scarab too many! We used 2 tanks, 2 healers, and 6 DPS. Our strategy was to have everyone group up and kite all the scarabs as a whole, while I stayed in the center shooting orbs, tranquilizing, and feign deathing any scarabs with me as their initial target. Give it a try with your guild!