Alien Earthworms

Alien Earthworms

Did you know that Connecticut, and all of the Northeastern United States for that matter, aren’t home to any native species of earthworm?

That’s right… by all accounts, earthworms don’t belong in New England. They are known as ‘alien’ species, meaning that although they may have taken up residence in our neck of the woods, they came from somewhere else altogether. In fact, their presence has caused some serious problems for forest ecosystems.

EarthwormSince earthworms are literally jam-packed into the soil, it may seem truly unbelievable that they haven’t always lived here. So before we explore just how these writhing invaders managed to cross entire oceans to make their home in our dirt, let’s examine how scientists are able to know that earthworms were nowhere to be found in the Northeastern United States as little as 600 years ago.

Beginning over 70,000 years ago, Connecticut and it’s neighboring states had been repeatedly blanketed by thick glaciers that engulfed almost every square inch of dry ground. Known collectively as the ‘Wisconsin Episode’, these series of glaciers literally demolished the landscape: mountainous rock formations were ripped apart, huge boulders were scattered miles from their original location by moving ice sheets, and gorges and lake basins were carved out of the ground. This glacial cataclysm literally pulverized the uppermost layers of frozen soil! Any earthworms that may have lived in the Northeast before the glacier took its toll would most definitely have perished long before the ice finally retreated for the last time roughly 11,000 years ago. When plants and trees once again began repopulating our newly thawed home, sometime around 9000 BCE, they did so in a territory that was entirely free of earthworms.

Ever since the last glacier retreated northwards, forests of the Northeastern US evolved in an environment where decomposition took place rather slowly. Each winter, the trees would lose their leaves just as they do today, depositing them upon the forest floor in thick layers. Without earthworms to quickly degrade this ‘leaf litter’, however, it would remain for a very long time. Not a great thing for hikers, but a truly great thing for Northeastern forests. This perpetual layer of leaf litter helped the forest floor retain moisture and ensured that pH levels in the soil remained suitable for the dominant woodland trees.

All was well in the forests of the Northeast for about 9,000 years… that is, until the first Europeans began making a long journey across the Atlantic Ocean to the shores of the New World. In an effort to establish colonies in this land, they brought some basic supplies from home to make farming a bit easier… probably a mix of cultivated food plants, herbs, and fertile topsoil. Hiding within these seemingly harmless materials were clever stow-aways that had always been very familiar to Europeans, but were nowhere to be found in the New World: earthworms. The rest, as they say, is history…

Of course, even in relatively modern times, Americans have inadvertently helped boost worm populations to the staggering proportions we find today. The agricultural industry has undoubtedly played its part, but the fishing industry also comes to mind… classic peddlers of everything from Canadian Night Crawlers to Red Wigglers. Whenever people toss these bait worms on the ground after a day on the lake, they are contributing to one of the most successful, large-scale takeovers of the Northeast that has ever been seen since prehistory. Oh, and in case you’re wondering, “Canadian” Night Crawlers were not originally native to Canada… they, too, were transplanted here from Europe.

Earthworms have caused a range of problems for Northeastern forests ever since they began multiplying in our soil. For starters, that layer of leaf litter that used to thoroughly cover the forest floor doesn’t last nearly as long as it once did. Worms are able to break down organic compounds at incredible rates, literally dissolving the leafy insulation which Northern forests require to retain moisture. In the process of devouring leaf litter, worms also fertilize the soil of the forest floor, making it especially vulnerable to invasion by plants that historically would have had little chance to survive. Remember, most of the wildflowers we ordinarily see in Connecticut these days are, in fact, not native to our state… one can only guess how much easier earthworms have made it for these plants to invade the lands of the Northeast. The problems don’t end there, though. Earthworms also work to neutralize acidic soil, creating unfavorable conditions for many tree species.

So, the next time you take a hike in the woods during late summer in New England, take note of how little leaf litter is left on the ground from the previous year. The next time you are digging in your garden and find dozens of writhing critters, consider that Native Americans who lived here less than 1,000 years ago would’ve been baffled to find such a thing even once in their lives. And the next time you go fishing down at the river, resist the urge to dump your leftover bait on the ground. Earthworms spread at a staggeringly slow rate… only about a 1/2-mile per century… but they can make up for lost time all too quickly if we inadvertently give them a helping hand.

References

“The Trouble with Worms”
http://www.wvnps.org/earthworms.html

“365 Urban Species. #083: Canadian Nightcrawler”
http://urbpan.livejournal.com/241995.html