You have clearly never dealt with a spider mite invasion.<p>They. Are. Everywhere.<p>They routine infest indoor houseplants, even in places you wouldn&#x27;t expect.  They&#x27;d find their way into a roof garden.  And because most predators require a wider range than most prey, there may not be as many natural predators available.<p>Commercial greenhouse growers definitely try to isolate their plants from invasion, but still rely on pest control when the inevitable happens.