How fast will flies fly?

The weather is heating up and the flies are out which really annoy the
hell out of me on long climbs. On these long climbs I've had plenty of
time to come up with a theory.

My theory is that (all brontosauruses are thin at one end ...sorry
couldn't resist) flies are only prepared to fly at 13kmh to land on me.
If I'm going 14kmh I'm not worthy of chasing and they leave me alone. Of
course that only applies if there's no wind. Anyone else noticed this?
How about a measurement to identify how stinky you are, eg. so stinky
flies will still follow you at 17kmh

DaveB