Little-known secret: Almost every earthworm in most of the U.S. came from somewhere else. Native earthworms all but disappeared more than 10,000 years ago, when glaciers from a Pleistocene ice age wiped them out. A few survived further south. But today, virtually all earthworms north of Pennsylvania are non-native.
This article discusses the benefits and harms of non-native earthworms in North American ecosystems.