An old treatment is to take a wad of tobacco, chew it up, and put that on the sting. It's supposed to take out the poison. Chewing tobacco, snuff, or tobacco from a cigarette is supposed to work.
When I was a teenager a neighbor broke his leg in a logging accident at tobacco harvest time. Relatives and neighbors gathered that Saturday to get his tobacco crop in. That's just what neighbors and relatives did. One of my jobs was to be about 25 to 30 feet up in the barn hanging the tobacco to dry. I managed to disturb a wasp nest and got stung on the back of the neck. It's amazing how fast you can get down from a spot like that when you are motivated. One of the men working there popped a dried leaf of tobacco in his mouth and started chewing. When it was wet he put that on the sting. I sat in the shade for a short while but it wasn't long before I was back up there hanging tobacco.
You find all kinds of wasp nests in those tobacco barns. You just hang tobacco around them to cover them up and they don't bother you. Obviously my technique was off that day.