When it's nice to fish, the mosquitoes get into the act

Good friend Bill Semion emailed from his place on the AuSable River after being chased off the river by hordes of mosquitoes.
"It's the first time I have ever had to leave the river because of mosquitoes," he wrote. Like a lot of fly fishermen, he fishes in the evening, sometimes quite late.
That is the witching hour for the large trout that like to sneak out from their cover and slurp bugs in the air, or as the float by on the waters surface.
But mosquitoes like we've been experiencing, can ruin a perfectly fun-filled experience. You can wear long sleeves, caps, slather on your favorite repellent and the things still come at you. And get some bug spray on your hands then change flies and you'll find fish won't like the flavor of Deep Woods Off.
Neighbors just home from an extended camping trip in the north complained about the bugs this year and how there seem to be so many more. Possible a result of the brutal winter?
I know everything was put on earth for a purpose but why mosquitoes and what good do they serve?