fun game. Pretty simple to pick up, I like the choice of ambiance instead of music. Good use of the limitation too and the basic shape graphics are a nice classic touch, I'm pretty sure complicated graphics would look cheap with this sort of game, but this really works well.
One small gripe is that I wasn't sure what caused me to lose lifes? Maybe I'm just a bit slow today and I know the description said "don't let them get away" but I didn't know that would cause me to lose a life. I intuitively though that since I'm eating the flies that me losing lives is somehow related to getting hungry and not eating enough, but that wasn't the case :D I figured it out on my 3rd attempt, but still, maybe if there was some sort of effect, like the fly going red for a second or something when hitting the edge, that would work as a good hint?