Tuesday, March 6, 2012

America's grossest invasive species

As if 12-foot pythons and lizards capable of biting off limbs weren’t enough for Americans (especially Floridians) to worry about, now comes a nonnative species that is not only harmful to indigenous flora and fauna, but also thoroughly disgusting. Meet the European earthworm (species of the genus Lumbricus) a grotesquely-long squirming squishy blob of an animal that is responsible for the decline in populations of the completely non-revolting ovenbird (Seiurus aurocapilla). It’s a bit backward sounding, I know, as birds typically eat worms, but the problem is more complex than ordinary predation or resource competition.

Happy, earthworm-free woods. Image: Duane Burdick.
The worms aren’t attacking the birds (they’re not that big) or even nosing in on their food supply. You see, the issue is that ovenbirds – a migratory species that nests in North America and flies south during the colder months – build their nests on the ground, and they do so in what was previously earthworm-free hardwood forest, which normally has a thick layer of understory plants. The abundance of low plants helps conceal ovenbird nests from predators, but now these nauseating euro-worms are ruining the delicate environmental balance.

Personally, I feel a titch misled. Being none too keen on earthworms from day one, I’d been told many times that we must appreciate (or at least tolerate) the slimy bastards because of all the good they do for plants. You’ve surely heard the same spiel. Worms’ subterranean writhing tills the soil, distributes nutrients, and makes gardens flourish. But such pro-worm propaganda, while true, is only part of the story. And what’s good for the garden isn’t necessarily good for the forest. That important understory foliage grows from the slow decomposition of leaf litter on the forest floor. Earthworms, which happily eat all sorts of rotting vegetation, feed on this litter and hasten the decomposition process. As a result, there is less fertilizer for the understory plants and subsequently less protective cover for ovenbird nests.

How did these clammy wriggling beasts from abroad worm their way into American soil? Like pretty much every other invasive species, they were delivered here courtesy of human sloppiness and/or cluelessness. European earthworms have been in the country as long as European humans, (you know, pilgrims and founding fathers and the like), brought in accidently by boat or deliberately by ambitious gardeners. More recent activities, logging and the dumping of fishing bait, delivered the pests into hardwood forests, where they’re currently running amuck. Yuck.

I don’t claim that earthworms have no place on our planet, or even in North America. Nor would I profess that any one animal was superior to another. I can only present to you the facts as I have uncovered them....

Images: U.S. Fish and Wildlife Service (L) and Michael Linnenbach (R)
I rest my case.

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