The Biting Fly Stomomyx calcitrans

 This cursed fly seems to be more common than it used to be.  To the unaided eye it looks like a rather small house fly.  With the aid of a super macro camera one can see more detail. The lower photograph shows the offending proboscis.  It is as hard as horn and can penetrate the soft skin of the human leg with ease, causing much irritation.
It is said that the skin is first cut using the lower lip of the labium and that is certainly how it feels.  The larvae develop in rotting straw or hay especially if it has been used as animal bedding and has been impregnated  with urine.