The Native and Invasive Earthworms

There was a theory that native earthworms from Canada were removed by the last glaciers about 10,000 to 50,000 years ago. It has been confirmed there are 19 species of earthworms that can be found in Ontario around the Great Lakes Region, 17 species originate from Europe and 2 species of earthworms from the United States.

However, recent research has shown that the native species of earthworms are present in Canada and they are species that survived during glaciation in unglaciated warmer soils on the west coast of the continent on the Queen Charlotte Islands, Vancouver Island and along the northwest coast of the United States. According to E-Fauna BC (2017), these native earthworms or “ancient earthworms” are forest-dwelling species found in the forest soils.

There are four native earthworms in British Columbia:
1. The native Arctiostrotus perrieri was the first earthworm described in British Columbia.
2. Arctiostrotus vancouverensis is the most widespread of four native species.
3. Bimastos lawrenceae appears to be endemic from a limited area on the west part of Vancouver Island.
4. Toutellus oregonensis distributes until the northwest coast.

To date, 24 taxa of earthworms have been identified in British Columbia. Eighteen of these species of earthworms are introduced by European species, primarily belonging to the family Lumbricidae, and they are potential to be invasive earthworms in the forest.

Earthworm has an ability to ingest and mix soils and is known for its contribution as food for wildlife and for use as bait by anglers. There are some reports mentioning that some earthworms infested the forest and dramatically changed by the absence of a leaf-litter layer and exposed mineral soil.

There are no methods to control earthworm populations in natural habitats. Preventing the new infestation of earthworms is the best protection. Such as: Dispose of earthworm bait in an area of known worm infestation such as the garden at home, rather than dumping bait on land in natural areas. The photo above: Earthworm spread by hook is the courtesy of Joel Saltore, National Geographic, Getty Images.

According to Ontario’s Invading Species Awareness Program, the impacts of invasive earthworms can be in three different ways:
– Earthworms consume the leaf litter of forests, causing tree seedlings, ferns, wildflowers, and potentially water quality to decline.
– Change the physical and chemical properties of the soil, adversely affecting many native species of plants.
– Change soil structure, inhibiting the historical and natural functioning of forest systems.

Earthworms can be separated into three major groups based on their feeding and burrowing habits: anecic, endogeic, and epigeic. The anecic species or the deep-burrowing earthworm species, inhabit more permanent burrow systems that can be found several meters in the soil. The endogeic species or the upper-soil earthworm species, move and live in the upper-soil strata and feed primarily on soil and associated organic matter. The epigeic earthworm species live in surface soil and litter or near the compost heap of green and brown wastes until only about 25 cm in depth.

Most of the invasive earthworms belong to the anecic and endogeic species that can live in the warmer soils. So, they will survive during the harsh winter and can escape from the predators such as moles, shrews, birds, reptiles, and amphibians. Among these earthworms, Lumbricus terrestris, L. rubellus, L. friendi, Amynthas agrestis, and Dendrobaena octaedra have been studied for their ability to invade previously uninhabited locations and disturb the local forest ecosystems.

The non-native epigeic compost worms or red wigglers are not potential to be invasive earthworms in the forest, simply because they will die in freezing winter. And during the warm summer they can’t escape from their predator due to the slow moving and cannot live in the soil. They are well adapted to the very variable moisture and temperature conditions that occur in the litter or organic waste layer.

Although their reproduction rates are high, they couldn’t survive long enough in the low-organic matter environment of soil. The most common red wigglers are Eisenia fetida and E. andrei. Their length is abou 8 – 10 cm, both are the earthworms species used for composting with worms or vermiculture (producing worm biomass or protein) and vermicomposting (producing worm castings or vermicompost), and they are adaptable in the compost pile. Red wigglers are also called trout worms that can be used as fishing bait for the medium size fish.

– Bintoro Gunadi

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