I would almost guess a Black Widow. Last year I found one in a place that I would have not expected to find a Black Widow, in an open field with its web strung between some tall blades or stems of grass. Usually I expect to find them under old boards and in barns and such but looking into them, the Black Widows, I found some that were not all black and had very beautiful markings, such as the one you have posted here. Not saying it is a Black Widow but it favors one. Creepy shot from my "phobic" point of view but very well taken.
