The question on Quora was:
My answer was:
Yes, it’s true. Earthworms aren’t native to North America, and they’ve done significant harm to North American ecology.
The invasion of European earthworm species across northern North America has severe impacts on native ecosystems.
These patterns suggest earthworm invasion, rather than non-native plant invasion, is the driving force behind changes in forest plant communities in northeastern North America, including declines in native plant species, and earthworm invasions appear to facilitate plant invasions in these forests.
Our results provide regional evidence that invasion by Lumbricus species may be an important mechanism in reduced plant-species richness and changes in plant communities in mature forests dominated by sugar maples.
(It’s more widely known that the introduction of honeybees around the same time has also devastated North American ecologies, to the point that we don’t even know what the natural ecologies were before the introduced bees drove the native pollinators extinct.)
In a comment to the question, I was asked whether earthworms and honeybees are beneficial. I said:
It’s context-dependent. For example, honeybees have driven many native North American pollinators extinct. That means that honeybees are required for pollinating lots of things. Are honeybees beneficial? Well, they’re essential, but they wouldn’t be essential if they hadn’t killed off their competitors.
Same with earthworms. Are they beneficial in your garden? Absolutely. Are they beneficial in the boreal forests that they’re invading? Not if you want to keep the forests as they are. So it depends what you’re asking.