What stung me?

So I did my dofe expedition yesterday and had just finished a 10 hour walk when I sat down to help my friend set up her tent, I then put my hand down on the ground(a quit woody foresty area) and felt an instant sting as if a small injection were going through my thumb. As soon as I felt it I lifted my had got up and just panicked and I completely forgot to even look at what had stung me but at that point I didn't care as my thumb started swelling and it felt like it was throbbing and burning and the pain lasted for about 8 hours possibly more.Does anyone know what this could be? It's definitely not a wasp or a bee as I've been stung before and it didn't hurt that bad or last for that long and it's not a sting nettle(as suggested by one of my wonderful teachers) as I had been stung by stinging nettles all day and it's not that bad. Any suggestions would be much appreciated :)