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Deadly Impact of Earthworms
Iím still getting over Farting Worms , and now this:
Worms in the Woods in which Chris Wedeles claims that earthworms are damaging his woodlot in Erin, about 60 kilometres West of where I sit and type these words. I say West, but WNW might be more accurate.
This blog is about Clear Thinking, not biology, but I admit a sense of gratitude to earthworms for eating leaf mold and making soil. Itís a bit of a chicken-and-egg situation, I know, but Charles Darwin said that earthworms made our soil, and I think he had a pretty good grip on the matter.
But I digress.
In the article the following text caught my eye:-
ďSlow-moving animals, such as earthworms, whose natural rate of spread is only about four to ten metres per year, remained in the south. Therefore, our Canadian forests evolved in the absence of earthworms.Ē
Now straight off, earthworms arenít slow movers; they fairly gallop along; my Red Wrigglers ( Eisenia fetida ) go like greased lightning when they are trying to escape from light.
Secondly, the spread of a colony of creatures is mostly independent of the speed of the critter. If a herd of elephants or a jamboree of jaguars maintains its population numbers steady, it will have no need to colonize new areas. Only if the population grows and the excess males and/or females get pushed out will the colony spread by cloning.
But then this stuck in my mind:
ďIn virtually all of Canada and much of the northern United States earthworms were extirpated during the recent (well, recent in geological terms) Pleistocene glaciations of 11,000 to 14,000 years ago when the landscape was covered with ice sheets up to several kilometres thick.Ē
The Wisconsin ice-sheet crept as far as Pittsburgh, almost. The Ohio river makes two sharp turns at Rochester and at Wellsville, turned back by the ice-sheet, so we can take Pittsburgh as an good local edge of the ice-sheet.
Google Maps tells me the driving distance from Erin to Pittsburgh via Buffalo is 528 kilometres, but of course thatís not in a straight line, but of course now would the worms pack a lunch and make a bee-line for Erin.
To a first approximation we can take 528 kilometres over 11,000 years and come up with 48 metres per year, a not-impossible rate of colonization (not movement) for earthworms; well within the bounds of possibility.
But then I am struck by another thought, and it is the chicken-egg thing.
Trees grow in soil. If earthworms make soil, which came first, trees or worms? Or did they arrive together, accompanied by raccoons, robins and squirrels and ... all the other things that crawl, climb, or slither in and around trees.
And where do the nematodes fit into all of this?
I have a problem envisaging trees marching inexorably northwards, breathlessly trying to outstrip their rivals, the earthworms.
I have no problem seeing a slow and steady creep of an entire ecosystem expanding, bringing with it native hunter-gatherers.
The SUVs and shopping malls came much later, but until they did, these old-stand forests were doing very well, thank you very much.
Toronto, Monday, August 03, 2015 11:43 AM
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