Mystery fly

There were 2 of these very small flies on a wild white indigo plant. At times it seemed they were either fighting over the plant or in some sort of courting display. I have never seen this type before. They have black and white wings. The bloom is just a bit over an inch long. Any ID will be appreciated.

Canon T3i
1/400 @ F-7.1 -0.3 adj ISO 100
Canon EF-100 macro USM
tripod.