Why Deer Flies Don't Like Yellow Lab Ears

German Shepherd puppy

Horse

Yellow lab puppy

Which one doesn't belong?

Deer Fly photo Copyright Biology Dept. of Randall & Schietzelt & Harper College

My mom and I were walking the German Shepherd puppy (above) and a yellow lab puppy (above) this morning in rural NY.  A nasty deer fly (huge bloodsucking crazed insect) was hovering over the Shepherd puppy bugging the poor guy to death.  The yellow lab, only feet away, never got bugged at all!

So I got a theory about how this devil's fly finds its target.  I remember reading that bees find the entrance to their hive by depending a lot on the shapes of the area near the hive, like what pattern the trees are in and other big shapes like rocks as orientation landmarks.  If the landmarks are moved, the bees have trouble finding the hive.

So, I thought, maybe deer flies use certain shapes as their guides.  The horse and Shepherd ears have a distinctive M shape and maybe the flies learned to go there since the skin is soft and vulnerable there.
 
If the deer flies depended on the shapes (vs. smell or just randomly landing on any spot on the animal) then that would help explain why the lucky yellow lab with droopy ears had no problems at all.