They are the nymphs, babies, of the box Elder bugs. They came from a Box Elder, Ash or another kind of tree.

http://www.en.wikipedia.org/wiki/Boxelde... If you enlarge the picture down the page, you can see the black on them.

At first they looked like aphid babies, but they aren't.

Box Elder bugs.............. you can spray them with soap and water and they will go away...........................