Something to do with Grass Clippings

Early this morning, before the full heat of the day, I mowed the lawn.  Having left it to grow for two weeks, I had to stop more frequently to empty the bag onto our compost heap in the back yard.  Like many times before, I noticed that some flying insects were attracted to the new piles of grass clippings.  They hovered around like the hymenoptera in a recent post, but on a much smaller scale.  So, after finished my duties, I decided to observe for awhile and learn a little bit.  Here is what happened…

This is what this swarming looked like…

Then I witnessed this…

In this video you will see a mating pair just above the center of the screen.  After moving around a bit you will notice another individual pester the couple.  Not long after the couple parts.  What I believe to be the male, flies off, while the female can be seen wandering through the grass clippings.  In one instance you may be able to make out that her abdomen in curled.  I hypothesize that she was laying eggs amongst the grass.

Here is another, longer, mating video.  If you watch long enough, after the female is mounted and released a second time, it appears that the male might be guarding her from other males.  It makes me want to research an easy method of capturing, marking, and releasing these insects to be more certain about what is going on.

In this final image it appears we may possiblly have a sneaker male.  Interestingly enough, this additional male appears to be smaller than the male that is mounted upon the female.  Look at the cicrumferance of the eyes (although I know that the perspective is not the same).

There you have it.  I imagine that this could be quite an easy observation to reproduce, all you need is a pile of grass clippings, and some of these insects in the vicinity.  In fact, students could most likely complete such an observation from home on their own.  I did notice that these flies were amongst the grass clippings the whole day and were even there in smaller numbers the following morning as well. 

Furthermore, it was quite easy to figure out what insect species these are using Insects in Kansas Field Guide published by the Kansas Department of Agriculture. 

So, what is the Order, Family, and species of insect imaged in this post?