To start, you'll have to catch a crawler hatchling from the mines to the east. Use the "Crawler Net" she gave you on one of these little spiders. Return to Maertha
She sends you to kill Kargail at the top of the ramp near the docks. Kargail is found at 361.46, 193.57, 512.27 . You need to walk at the road for some time to spawn him. He runs up the ramp and stops up above. You can't hail him until he stops. Then, the spider is to feed on the body. Use "a crawler hatchling" from your inventory. He'll eat his fill, then you click on him and you'll pick him up.
Return to Maertha.
She tells you to release it at the entrance to the mines. When you do it goes on a killing spree. Killing everything in the mines except the foremen.