Alex notes that earthworms are a hot topic in the forums; the Spring issue of Ontario Nature Magazine looks at the subject of invading European earthworms, and Sharon Oosthoek writes that the very trait that makes the works the darling of gardeners everywhere makes them a menace in the forests. Evidently they are much better at munching through leaf litter, causing nutrients to leach away in the rain instead of binding them up in organic matter.
Map from New Scientist; click image to enlarge
University of Minnesota ecologist Lee Frelich calls it another effect of climate change, because while worms are slow, moving north at a rate of 5 to 10 meters per year, trees are slower. Oosthoek writes:
While European worms have been here for more than two centuries, according to Frelich it takes roughly 1,000 for a hardwood forest to adapt to such a drastic change. An, as the climate warms, these worms are thriving farther north.
But the real culprits in introducing worms into northern forests are probably fishermen transferring bait from one lake to another. Yet another reason not to fish.
More in the New Scientist on the War of the Worms, which warns that another worm is on its way:
This time it's a pencil-sized Asian species of earthworm from the genus Amynthas, which makes particularly good fishing bait. This enemy is big, has a voracious appetite for leaves, and, says Paul Hendrix of the University of Georgia in Athens, who is studying the problem, wriggles along so fast, "you can almost hear them moving through the litter". Local worms are advised to dig in and prepare to do battle.