Cute! Hits on the theme perfectly! And the movement controls felt fantastic. Something about it just made me want to move left and right all the time. It felt so satisfying. And considering that's the main mechanic of the game, you nailed it.
I did find it feeling a bit unfair at times. I'd be doing my best to get away from a fly and it would just move horizontally to hit me. So if I grew all the way to the left and the fly chased me from the right, I'd have no way out.