Another insidious and under-rated enemy of wild plants in NE North America is the earthworm. These, like honeybees, are introduced from Europe, and they are systematically destroying the duff layer of N. Am. woodlands. This layer is needed by many wildflowers, which are disappearing in large measure thanks to these worms (and also thanks to the overpopulations of deer due to elimination of natural predators and limitations on hunting).