This is such a fun concept that's simple in all the best ways! If I'm correct it feels like your parasite drains you each time you make a shot, which is great since it makes you have to pick your shots carefully. The animations are so cute. The music is awesome too!!
I also like that you added a high score counter on the main menu, though I think having the score visible while playing the game would be great. I also think I found a funny exploit where if I just let them all swarm onto me but I keep spam-clicking, I could live forever. Also this would make a great base for a simple rogue-like :)) Loved this!!