These are charming little flies.  The habitat they live in--not so much.

We have a large dog and a large area for him to run.  Dogs being dogs, he finds things and likes to bring them up into the yard.  Things like deer legs, with parts of their flesh and fur still attached.  Our dog has gotten sick from eating rotting flesh, probably from road-killed or hunter-killed deer.  So we take those things away from him.

Once you have a big old smelly deer leg, what do you do with it?  It is not a good thing to haul it somewhere and dump it.  You can't just put it in the garbage.  You can bury it if the ground is not frozen.  But it was winter time.  I put it in the bed of an old truck to keep it away from the dog and partially covered it with plywood, with the intention of burying it in the spring.

Over the winter, there was more than one leg, and a number of other body parts. 

In the spring I examined the various parts to see how big of a hole I needed.  There were a number of flies, but these caught my attention.  The males have big, long antenna that sort of resemble antlers or horns.  It was fairly easy to determine by their behavior which ones were males and which were females.  The females (below) have shorter antenna--about half the length of the antenna of the males.

 The flies walk quite rapidly--they move so fast that they are hard to photograph.  They seem to like walking along sticks and bones.  You can see the males chase other males away from certain areas.

The flies live in carrion, but more specifically seem to lay their eggs at certain areas of the bone, and the larva live inside the bones, feeding on the bone marrow.

These flies are often seen on deer and moose carcasses.