The Stinger Pit is an event that can be found in Ruins of Corvus in Diablo III. The unique monster Scarnax must be defeated to complete the event.
The event always occurs near a pit (more like a hole in the floor) of the same shape. Dozens of scarabs climb out of it, led by Scarnax. Until he is killed, more and more of his pack will arrive.
The battle is especially complicated by the fact that scarabs block pathing, making players vulnerable to Scarnax's attacks.