Invasive Worms Of North America
A few days ago I discussed identifying Alabama Jumpers. Amynthas species have been rather controversial over the last few years. Being a tropical species it wasn’t expected for them to show up and survive in Northern States such as Wisconsin, Illinois, Michigan, Vermont and others. The adult worms actually are not believed to survive winter but the cocoons do. So what’s all the hubbub about Amynthas agrestis, Amynthas gracillus and the northern states? Theres a lot written about it but none of the sources seem to explain it thoroughly.
For those of us who vermicompost and add castings to our gardens, the idea of worms being destructive to the environment seems absolutely ridiculous.
I’m going to try and explain the logic behind this based on hours and hours of research and reading.
During the Ice Age glaciers descended over North America all the way down to regions of southern Ohio, and northern Kentucky. This eliminated all indigenous earthworms from the northernmost part of the continent. For over 1000 years after the last Ice Age ended the plants and trees that began to repopulate the north did so without worms in their soil. Fallen leaves and branches were decomposed slowly by primarily fungi. The plants (trees in particular) in this region evolved to thrive in this thick, fungal rich humus and deep leaf litter.
Onto the scene come the European settlers, their ships ballast of soil containing worms brought accidentally from the homeland. Lumbricus terrestris, Apporectodea longa and other species were soon finding their way into forest litter and newly cleared farmland. It seems likely the European introduced worms were similar to those that had been wiped out so minimal damage was done and a balance was quickly reached.
Scroll ahead in time to the introduction of Amynthas species in potted plants from Asia. These tropical worms were never believed capable of survival in the harsh northern winters. Suddenly they began to move north, perhaps again in potted plants or in fishemen’s bait pails. These worms are from a very different climate and have very different feeding habits. Worms of the Amynthas family prefer a similar diet to fungi, like leaf litter and rotting wood. Worms can eat these materials in a fraction of the time that it takes fungi to break them down. Amynthas excrete enzymes that cause faster decomposition of cellulose and lignin (even when the worms are gone). Leaf litter and fallen branches that are habitat for woodland creatures and insects are quickly reduced to worm castings, endangering relationships in the forest.
The quick conversion of food previously used by fungi endangers the fungi and their mycorrhizal relationship with the forest plants and trees.
The previously thick layer of leaf duff offered protection to plant roots from water erosion and freezing temperatures. Now being worm castings water penetrates and soil begins eroding soil form around plant roots and exposes them to colder temperatures than when there was an insulating layer.