A garden can represent the world in a miniature. Given time and energy one person can keep it in order.
But though many millions of people write, speak and demonstrate for peace, justice and order in the world, they do not have the same success.
A parallel can be drawn between a powerful country which goes beyond its stated desire to bring freedom and democracy – killing large numbers of people living in other countries – and the slug, which goes beyond its beneficial task of clearing debris and kills many plants.
A country which wants to corner oil and other raw materials, at whatever cost to others, is like that variety of knotweed finding its way into many countries and growing over its weaker neighbours.
Slugs, wild plants and powerful countries can play beneficial roles but both, at times, are invasive species which cause a great deal of damage and are very hard to control in a humane/non-toxic manner.