If you include eggmorphing, which would allow a lone facehugger to regenerate a whole nest, then a xenomorph infestation on Earth or any colonized world could be very hard to stamp out. They can nest pretty much anywhere, in a forest, a warehouse, or an underground burrow in a desert. And even if you go into a large nest with guns blazing and kill the queen and all the drones, all it takes is a few facehuggers to escape to have made the effort for nil. And facehuggers almost certainly would escape, since they're small, fast, and they probably instinctually flee when they sense they're being overrun so they can start over somewhere else.