Yeah I thought I might have made it a bit too difficult in the end - I probably would have done some sort of progression with ramping up of difficulty if I had more time - classic case of the developer being the only playtester!
There is a 'health bar' that gradually decreases and is topped up by catching the flies - but I definitely made it too small and tucked away in the corner where it was not clear enough what was going on.
Thanks for the playing and for the feedback!