This makes sense since most of the mites are not in contact with the fly.
So in this case the mites are waiting for the fly to lay eggs -- much more efficient then hitching with a beetle. Very clever way to obtain dinner.

Do you have any idea who the fly is in this case?

Thanks, John. Great help, I really appreciate it.

Lynn

Sorry, just bad guesses. My guesses go - I think that Calyptratae is likely, then I feel good about taking the Muscoidea branch, I timidly take the Muscidae path, I am tempted by Coenosia but resist because the wing veins seem wrong, then I look at this diagram and I wonder about Stomoxys calcitrans (Stable Fly) but I think that your proboscis is wrong for that, Muscina stabulans is listed at Neartica but we don't have any here, then I wonder if I just got lost.

I really enjoyed reading your thought process and had to go follow your path. Thank you for doing so much detective work on this fly and writing it with such a sense of fun adventure.

I've added 3 more images.
I can Frass some of them later.

Here's a quote I found for Muscina stabulans: "The false stable fly is not a blood-sucker and has sponging-sucking mouth parts like the house fly."
at: http://www.icb.usp.br/~marcelcp/muscina.htm
Can we rule him out?

To my very untrained eye the stable fly looks very good, even the proboscis. You didn't mention what wasn't looking right about it. I thought maybe because she didn't hold it out horizontally like the most of the ones pictured, but then she was busy at flowers.

There are several horse stables here a half mile as the crow flies and a little further a buffalo farm. So that works.

What might not work is that she was busy with flowers instead of biting livestock.
Also I don't know what other look alikes might be out there or what hidden anatomical features there might be that need consideration.

Based on physical appearance alone without knowing what is most important to look at, and looking at a lot of flies, Stomoxys calcitrans (Stable Fly) looks like a perfect match. In my non expert opinion I don't think you are wandering.

Here is Matthew Ireland'S photo with distended proboscis for comparison:

for some reason this looked wrong

but this looks totally correct

The first one just didn't look like the old "phonograph needle" that I always think of. Must have been the angle that confused me.
Good to see that it got an ID.