Whew, that is really tough, they have quite a bit of health, it seems like. xD
they have shared health. you can only hit them when they came down on you. I rly should have made a tutorial level sry xd. if u use the spray on them 4-5 times it should be enough.
Oooh, only when they are down? That explains it, I was trying to hit them when they were in the air. :P