Fun fact:

Earthworms were all but wiped out in North America during the last ice age. The earthworms in North American soil today are almost all European. They're still spreading out and moving North in Canada.

Mindblowing Implication:

Prior to the introduction of European earthworms, dead leaves and other detritus just sat on the surface and accumulated until it was several feet deep in forests. Native plants often took advantage of this slowly decomposing source of nutrients. Earthworms break that detritus down into humus much faster, often starving native ground-cover plants and feeding invasive species. We're still watching a massive change to ecology, that started at the time of European contact, slowly unfold.