Mississippi Valley Field Naturalists
October 24, 2012
The Lowly Worm
The Mississippi Valley Field Naturalists’ (MVFN) 2012-2013 public lecture series, Nature Beneath Our Feet, continues November 15 with the third presentation, “Earthworms: Whose Friends are They?” You do not need to be an expert to enjoy the presentations—just possess a curiosity or appreciation for wild nature. Cottagers, hunters, fishermen, canoeists, hikers, campers, artists and seasoned field naturalists alike will find something to interest them as we explore what lives in Lanark County and how best to protect it for future generations. Refreshments are offered at each lecture.
This lecture will be presented by Paul Gray from the Applied Research and Development Branch, Ontario Ministry of Natural Resources, Peterborough. He is an author of the recent publication Implications of a Potential Range Expansion of Invasive Earthworms in Ontario’s Forested Ecosystems: A Preliminary Vulnerability Analysis.
Earthworms and beavers have more in common than you may realize. Both are described as “ecosystem engineers” because of their abilities to make significant changes in our environment. The underground burrowing systems that worms create increase the amount of water and air that reaches plant roots and other soil organisms. Also, earthworms mix the plant litter and organic matter into the soil, increasing the speed at which they decay and release nutrients. No wonder gardeners love them!
The last glaciation eradicated native earthworms from Ontario. Our forests developed in the absence of earthworms until they arrived with soils (for ballast) and plants brought here by European settlers. Since then both adults and cocoons (egg cases) have continued to be spread through dumping of unused fish bait, transport of compost, mulch, and top soil, movement of landscape plants with soil around their roots, dispersal from tire treads, and road building that involves bringing in soil from elsewhere. At present, 17 non-native European and two North American (non-native to Ontario) earthworm species survive in the province.
Beyond the garden, in native forest ecosystems, earthworms are very bad news. They significantly alter forest soil structure and chemistry, reduce nutrient availability, and decrease the diversity of understory vegetation, soil fauna, and belowground fungal communities. That is, they reduce and destroy habitat for native species.
There is also evidence that changes caused by earthworms lead to a cascade of other changes in the forest that affect populations of small mammals, birds and amphibians, exacerbate the impacts of herbivores such as white-tailed deer and facilitate invasions of other exotic species such as slugs, European buckthorn, and garlic mustard. Thus earthworms pose a serious threat to the biodiversity and long term stability of our forests. With a warming climate, the potential for some earthworm species to expand their distribution or expand populations already established in forested ecosystems will increase, likely resulting in further significant ecological changes and socioeconomic impacts.
Because earthworms are spread mainly by human activities, there are some simple things you can do to prevent their further spread—take unused fishing bait home with you and freeze the container for at least a week before discarding the contents, freeze (as previously) compost before using it, wash ATV or other soil-holding vehicle tires before transporting the vehicle, join the Great Lakes Wormwatch citizen science effort (http://www.naturewatch.ca/english/wormwatch).
Interested in forest conservation? Get “the dirt” on earthworms at Paul Gray’s lecture “Earthworms—Whose Friends Are They?” and spread the word to your friends and neighbours. This MVFN presentation will be held at 7:30 p.m on Thurs. Nov. 15, 2012, Almonte United Church, 106 Elgin St., Almonte. All are welcome ($5 fee for non-members). For further information please contact MVFN’s Program Chair Cathy Keddy at 613-257-3089.