No more (wingless) Feral Beasts?

I had lots of them hidden behind and between buildings. They seem to spawn from the edge of the playing field, and if there is a building in the way, they get stuck.
Since searching and clearing the hidden ones they spawn again in my town.

They are difficult to spot, because they get transparent with the buildings. Look for movements. It would be nice if the falling leaves could be disabled while searching for them.