I think you literally made 100% of the first half of this up
There are no earthworms that used to be here; read the article. Crazy worms do exactly the same thing (remove the layer of leaf litter that traditional NA boreal forests depend on), they just spread a little more quickly which makes it a little more of a problem. But the essential issue is the same. And I don't think killing either one of them makes any difference at all; humans will not encounter either one on anything even remotely similar to the scale that would make going after them on an individual level a useful thing to do.
Edit: Okay I am totally wrong; the article talks about northern forests only, and what I'm saying isn't true of the US / North America as a whole.
Oh shit
The plot thickens
Now I'm confused. Here's what Wikipedia says. The last ice age was 11,000 years ago, so presumably they should have spread back out northwards since then... or maybe they needed to evolve the ability to survive in the cold first, which they haven't had time to do? IDK.
I'll edit the title to be more accurate. I don't necessarily see a conflict between the fine details of what the article says / what Wikipedia says / what Smithsonian says, but my title is misleading and the careless way I read the article led me to totally misunderstand it.