Some costly and a couple of dangerous solutions above. Cheap and 100% effective is to:
Wait until dark and dump three heaping tablespoons of Sevin powder down the hole. All gone in a couple of days. Dead all gone.
A quicker but a little more dangerous way is to:
Wait until dark and point a lit propane torch at the mouth of the hole and start thumping the ground around the hole. They will come streaming out and be singed in the process. This will take a few minutes and don't drop the torch or move away from the hole.
The lawnmower method does not get them all.

