This was a really neat idea. I looked at the screenshot and thought "Oh, ok, it's a tower defense." Then I read the instructions and thought "Oh, ok, it's more like one of those lane-based army generator games." Then I started playing and thought "Oh! Ok, it's actually a herding game." And in the end, even that mould doesn't quite fit because after a while, the humans are so terrified that they herd themselves out! XD
I'm sure this wasn't your intention, but it literally kept me guessing until the very end, in a good way. Neat!