February 2021 – The Real Dirt On Worms

What if I told you that earthworms were devastating forests all over North America? We have all come to know worms as being extremely beneficial in our gardens by aerating and fertilizing the soil, but there are some varieties of earthworms causing irreparable damage.

Over 10,000 years ago, the Ice Age covered the land masses of North America and killed off most of its native species of earthworms. The first European settlers of the 1600s brought hitch-hiking European earthworms in their imported plants. Trade and economy brought other species throughout the years in imported soil, mulch and fishing bait, and now there is a diverse population of Asian and European earthworms throughout North America.

Forests in North America had adapted to growing strong without the aid of earthworms, and are naturally very aerated. The layers of slowing decomposing leaves on the forest floors not only fed the trees, but protected their roots from erosion and disease. In fact, with the influx of the new varieties of earthworms, many of the healthy forest floors are now decimated, as the worms devour the leaves, which in turn releases carbon dioxide into the atmosphere and robs the soil of beneficial carbons.

Several birch, red oak, poplar and maple hardwood forests which previously had generously thick layers of organic protection and food, are now littered with bald patches from earthworms munching down. This has limited the survival of forest seedlings and negatively impacted the biodiversity of smaller plants, insects and reptiles on the forest floor.

Peter Groffman, Senior Scientist at the Institute of Ecosystem Studies in Millbrook, New York stated “what we’ve seen in these forests that are invaded by earthworms, they have less humus than forests without earthworms because it’s almost like tilling the soil. You’re mixing the organic matter, you’re stimulating the microorganisms that are degrading the organic matter. And so we found that in the forests invaded by earthworms, they were losing 25 percent of the organic matter in the surface soil”.

Several scientists with funding from the National Science Foundation have been studying forest soils in the northeastern US, and it was discovered that where patches of bare forest floor were found, it was symbiotic of invasive earthworms from Asia and Europe colonizing the soil.

While Groffman agrees that worms can be of benefit to compacted soils through aeration, he continued to say “Some of my colleagues have been involved in work on earthworms in agricultural systems, and manipulated levels of earthworms to see was there an improvement in the environmental performance of those systems. And they were unable to find any.”

“And in fact earthworms, you know, by making holes in the soil, accelerate the movement of water through the soil. And so in a certain way that’s good, and it stimulates infiltration of water into the soil, but it also stimulates leeching of water through the soil profile and into the groundwater. So sometimes we might find actually more water-quality problems in gardens or in agricultural systems because earthworms are accelerating the way water and nutrients move through the system.”

It is important to note, that there are over 5000 species of earthworms globally. Only an estimated 16% of Asian and European species are damaging, as reported by Scientific American. Even more interesting, it is just recently that researchers have discovered that the ice age didn’t abolish all of the original species of earthworms.

Research has proven that the ice did not cover Vancouver Island or Haida Gwaii, leaving some species of naturally occurring earthworms in these specific areas. Researchers have termed these native earthworms ‘ancient earthworms” (Marshall and Fender 1998). Unfortunately, most of the natural species left are not often seen, and it is the larger, more aggressive Asian and European species that have taken over.

Increasingly popular is vermiculture and the use of worm castings manure is one of the best ways to add nutrients to soil. So are these worms bad too?

Red Wigglers, Eisenia Fetida are originally from Europe and are bred because they are an aggressive and quickly reproducing worm that assists with decomposing organic material. They are commonly used in composts as they adapt well to warm environments, and they feed on the organic matter, bringing it to the surface of the soil, and leaving castings and organic material behind. Gardeners harvest that material which will greatly improve soil fertility.

According to an article published by the Great Lakes Worm Watch, “Fishing bait should be discarded in water, not on land and worm castings from compost bins should be frozen before being used in gardens”. This will ensure that invasive earthworms are not released into unnatural environments, and through freezing castings for one week, any worms and their eggs will be killed.

In a controlled environment, earthworms can have great uses, but letting them go wild may have repercussions on our natural environment.

Angela Hicke – Van Isle Wild

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