Observed on cool night (53 deg F) on outside of compost bin. At 3-4 mm it is small for M. polita, also the forelegs and antennae are nearly all yellow instead of mostly black. It is therefore likely M. flavicornis or M. flaviventris, which are difficult to distinguish in the females (can tell this is a female because the eyes are separated). According to Woodley https://doi.org/10.4289/0013-8797-111.2.527 "the middle femur in M. flaviventris is wholly yellow, while it is marked with black to nearly wholly black in M. flavicornis and M. polita." My interpretation of the side-view photo is that the middle femur is wholly yellow, so I am leaning towards M. flaviventris. There is also a difference in wing venation related to the closure of the discal cell; it is less conclusive from my photos here, but having looked at pictures of m. Flavicornis wings, they really have a strong outline of this cell that is missing here.