This question refers to the Google-sponsored AI Challenge, a contest that happens every few months and in which the contenders need to submit a bot able to autonomously play a g
I think your problem can be solved by turning the problem around. Instead of calculating the best moves - per ant - you could caclulate the best move candidates per discrete position on your playing board.
That would scale in a linear way - but have some trade off in not providing best individual movement.
Maybe worth a try :)