Gary "thinks" it was fire ant bites??? Excuse me, but you KNOW if you've been biten by fire ants. There's no thinking about it. There's a reason they're called "fire" ants. I still think he was looking for an excuse to leave.
I believe Gary's "think it was the fire ants" had to do with his being sick and unable to continue in the game. I do not think it had to do with whether he was bitten or not. 'Cause you are right... you know when a fire ant has bitten you.