Are flies more cunning than I gave them credit for?

While reading my book or newspaper outside I am visited by (house)flies all the time these last several weeks.
They annoy me.
Now I found that most of them, most of the time, land on my shoulder or upper arm, when there is plenty other bare skin available.
When I grab the fly sweeper (is that a word?) they seem to notice it because from that moment on they quit their attacks.
Until I lose concentration and put the sweeper away.
Next thing I know they’ll come back again.
So, are they visual that good?
Can they think or reason?
Do they communicate (warn each other for the dangerous fly sweeper)?
And do they prefer the shoulder because that seems to be a difficult place to reach for me?