Speak to Kushuk in Kor-Gursha.
Kushuk tells you, "Those Guruk Smashers keep destroying our fungal store houses. You should hear them laughing. I've gotten pretty good at hunting them, but I could really use your help. They hide out in the Eastern and Southern Catacombs. Track down and slay 40 of those infuriating Guruk Smashers and I'll reward you well."