Ever since the publication of The Formation of Vegetable Mould through the Action of Worms with Observations of Their Habits by Charles Darwin, the European Earthworm Lumbricus terrestris has had a pretty good press.
Darwin may not have been the first to appreciate their value: Aristotle called them “the intestines of the soil” . And very valuable they are, this side of the Pond. Though they are not getting it all their own way. According to Wikipedia:
In parts of Europe, notably the Atlantic fringe of northwestern Europe, they are now locally endangered due to predation by the accidentally introduced New Zealand flatworm and the Australian flatworm. These predators are very efficient earthworm eaters, being able to survive for lengthy periods with no food, so still persist even when their prey has dropped to unsustainably low populations. In some areas, this is having a seriously adverse effect on the soil structure and quality. The soil aeration and organic material mixing previously done by the earthworms has ceased in some areas.
However, their reputation has suffered a bit of a bashing in parts of North America, where they are found not to do so well in agricultural land.
L. terrestris is considered invasive in the north central United States. It does not do well in tilled fields because of a lack of nutrients, pesticide exposure, and physical injuries from farm equipment.
and are harming forest ecosytems:
The species, however, thrives in fence rows and woodlots and can lead to reductions in native herbaceous and tree regrowth.
Now another charge is laid at its door. The Smithsonian Migratory Bird Center tells us:
Minnesota and Wisconsin appear to have lost any worms they may have had during the prolonged and severe glaciations which affected North America. Since then, fungal systems have developed in the maple-and-basswood forests which slowly decompose the thick layers of leaf litter. These have provided good soil for a variety of herbaceous plants, among which the nests of the Ovenbird can be well hidden.
Along comes the earthworm, brought to those remote forests by loggers and fishermen, and rapidly eats and digests that leaf litter. And now the forest floor is largely bare soil, and the few plants that grow there do little to hide the nest. Also, the number of insects declines, so the bird requires a larger territory, leading to smaller populations.
(from the Smithsonian article)
The researchers found no decline in three other species of ground-nesting birds included in their survey – the Hermit Thrush, Black-and-White Warbler and Veery – nor did they find a correlation between Ovenbird decline and invasive worms in other forest types, such as red oak, paper birch and aspen.
So I ask – why is the combination of ovenbird, maple-basswood and earthworm so problematic?