Are earthworms a destructive or benign invasive species in North America?
Earthworms came over here with the tobacco trade. http://www.charlesmann.org/articles/NatGeo-Jamestown-05-07-1.htm
There is very little evidence that they help garden soil. True they are found in most good organic soil (Many chemical farmers have found that the chemicals they use can kill off most earthworms in their soil.). But are they merely taking advantage of all that good mulch and manure you so carefully spread or are they aerating and spreading nutrients in the soil?
I'm undecided. When I first started farming on this very rocky land there were very few earthworms. We have this weird shale rock that breaks down easily when plowed or even walked on. As the shale breaks down and turns to soil, more earthworms come around. But even without them, I was able to grow most hardy vegetables using heavy mulch, because of all the water we get. Now I have more real garden like soil and the worms are all in it.
I understand that in the forests of North America they altered the mulch layer so much that many species of trees died off and struggled to survive. A gardener I once knew hired a yard service that would put down mulch around the trees once a month even if they didn't need it. Some of those trees had 3 to 4 feet of mulch around them and were doing better than those with just inches of mulch, especially during the drought.
So, what do you think of those wiggly crawly things?
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