Forests under threat from exotic earthworm invasion: Study shows humans to blame for spread of non-native species

Their findings, published online in Springer's journal Human Ecology, suggest that humans spread earthworms both inadvertently via horticulture and land disturbance, in the tires and underbodies of vehicles, but also knowingly through composting and careless disposal of fish bait.

Non-native species of earthworms can have a detrimental effect on the flora and fauna of the forests. They can be responsible for accelerating the breakdown of the organic material on the surface of the forest floor, thereby reducing the habitat for the animals living there and possibly increasing soil erosion.

The researchers conducted a case study in Webb, NY, a large township in the Adirondack State Park, home to the largest unbroken temperate forest in the world. They first analyzed the environmental history of the area and followed this up with a mail survey of 150 Webb residents to assess their recreation and environmental practices related to earthworm dispersal.

The authors found that the introduction of exotic earthworm species can be traced as far back as European settlers arriving in North America and dumping ship ballast, a mixture of soil and gravel, onto the land. Today, the main culprits are recreational fishing, gardening, composting and the movement of egg cases on vehicles which are mostly to blame for their continued spread.

The authors conclude that even the most environmentally conscious individuals do not currently realize what a threat these earthworms pose. They suggest that, in particular, gardening clubs and convenience stores which sell worms to anglers should be targeted with information and that "the public needs to be empowered to implement behavior that helps mitigate the introduction of earthworms."