What Causes Red Spots On Thighs?

I was up in some hills in southern california in the Glendale Area, at a lookout point . You kind of have to walk up some steep terrain, mud, bushes that kind of area. At the top we sat down on some dirt and i felt a stinging sensation on my Knee, it was pretty painful, the shortly after on my other leg on the thigh. I must assume it was a bug on the ground but I am not sure what. I think there was some ants, maybe fire ants, do i need to be seeking immediate medical attention? The pain stopped after about a hour and a half, it was kinda a stinging consistent pain, my right thigh more then my knee. As of know about 6 hours later there is just a small nickel sized red circle-ish spot and on my a thigh a slightly larger spot, a little bigger then a quarter. So do i need to seek medical attention?