As gardeners, we are well aware of the pro-worm propaganda that has been engrained into our psyche from an early age. While the benefits of worms in an agricultural setting have been well documented, it would seem that worms in North America have a downside. Unless you live in the southeast or parts of the Pacific Northwest, your region has no native worms. Wiped out by the Pleistocene glaciers, vast regions of the continent have evolved without worms present, which has left a considerable legacy on the soils as well as the plant species that rely on them. Originally introduced in ship ballast during the first European excursions to this continent, worms have since invaded wild areas around North America and are wreaking ecological havoc. That’s right, worms are bad for our native plants. The negative impacts of worms are first felt in the most obvious place, the soil. Their burrowing activity mixes organic and mineral soil layers and allows for greater infiltration of water. This leaches valuable nutrients from the soil that plants, especially forest herbs, desperately require. It also increases runoff and erosion. Worm feces, or casts, speed up microbial activity as well, which eats up vital stores of nitrogen in the organic soil layers. Worms also speed up decomposition of soil litter by pulling leaves and other organic materials down into their burrows. The loss of carbon from areas where worms have invaded has been likened to a complete functional loss of the forest floor. Even trees suffer as the microbial community and the rhizosphere are permanently altered. Worms have also been shown to eat vast quantities of small seeds, especially those of our dwindling orchid species. Recently, evidence is coming in that worms also serve as disease agents. They can be either primary or intermediate hosts to a wide array of viruses and parasites that affect small mammals, birds, and even humans. One high profile case has shown that worms are even a vector for the virus that causes foot and mouth disease. Currently the US has no restrictions on the import of worms. Because of this, new invasions are happening every year. Research has shown that epicenters of worm invasions are significantly correlated with roads and fishable streams. The best way to slow the spread of worms into new areas is to not release them. Worms are very slow to expand their populations, often moving less than 5 meters a year. Humans are the most considerable vectors for worm movement. Simply by not discarding worms used for bait, composting, or around the soil of potted plants, we humans can at least slow their rampage across this continent.
Photo Credit: Michael Linnenbach