The Jam Boys sole purpose was to keep the mosquitoes away from the golfer. To do this, the Jam Boy would cover himself in Jam to attract the mosquitoes away from the players. When the game was over the Jam Boy got to keep the jam he was wearing to take home to his family.
And for trivia, it is still possible to hire a jamboy in some countries!
Nick: Dude, I was thinking the exact same thing.