The invasion of non-native earth worms poses a complex ecological threat to North America. Earthworms are an integral part of agriculture, aerating and letting water and other nutrients penetrate the soil with the underground tunnels made, and fertilizer from their waste products.  Earthworms also produce net decrease of CO2. As a result of the services earthworms provide, people looking to capitalize off of them have brought earthworms from all over the world to North America.

Lumbricus rubellus HC1

The non-native species have successfully enhanced the agricultural economy in some places, however there are other cases where the alien earthworms have dramatic impacts on ecosystems. The alien earthworms are more likely to consume above ground leaf litter which harms the plants, amphibians, and insects.  “Leaf litter provides many nutrients for the plants and animals” on the lower ends of the food chain, like primary and secondary consumers.  These earthworms can also change the microbiomes of the soil, which can cause serious harm to the plants in the area and indirectly affect other animals.  Microbiome changes appear in pH shifts, nutrients, and even texture, all leading to poorer plant quality and health.  Without the main players, producers, functioning at peak performance, the ecosystem can begin to waver.

To make things even worse, some female alien earthworms can reproduce without fertilization from a male. Faster reproduction, independent of males, contributes to better ecological fitness.  Different species of earthworms exhibit varying levels of fitness. This is not due to their gym habits, but rather because they have evolved to survive and reproduce more effectively than others. Additionally, as a byproduct of climate change, there is new inhabitable land ripe for the alien earthworms to dig their way into.

“Despite all this, only a limited number of studies have documented alien earthworms’ spread, and none have covered colonization dynamics over a large spatial scale or a large number of species.” A new database using records from 1891 to 2021 of native vs. alien earthworms, was used in tandem with another database of U.S. border interceptions of alien earthworms between 1945 and 1975. The new technology powered by ‘machine learning’ aimed at finding the non-native earthworm introduction and spread. Researchers have found that in Canada the alien earth worm population is three times greater than the native population, and in the US and Mexico there are 2 native earthworms for every non-native earth worm.

In AP Biology, we have explored ecology, including concepts such as trophic levels, food webs, and ecological fitness. Trophic levels and food webs directly related to the Alien earthworm threat because a dip in low trophic levels, especially producers, have catastrophic effects on the ecosystem of a certain place.  For context, a trophic level of an organism is the number of steps away from producers it is, ex a primary consumer in NYC are crickets because they only eat grass a producer, and a food web consists of all the food chains of an ecosystem.  An important thing to note with food webs and trophic levels is each trophic level only can gain ten percent of the energy of the last trophic level.  So, if an ecosystem lost significant plant growth or biomass, the trophic levels above it would have less energy and the population sizes of the organisms living in the ecosystem would shrink.  The harmful alien earthworms damage ecosystems by targeting plant mass and soil nutrients which gives each trophic level less energy, effectively shrinking the entire ecosystem.

This topic intrigued me because of how closely related it is to what I have been learning in class.  I also enjoyed learning and writing about how such a seemingly small change in an ecosystem can have impacts much larger than themselves.  I also find human impacts on ecosystems interesting to learn about.  I found this one to be especially interesting because of course something like the industrial revolution had huge long term impacts on the ecology of the world, but you wouldn’t immediately think something trivial like earthworms would have much of an impact on anything, or be so different from one another that they can change the pH of the soil!  What do you think: are alien earthworms worth paying attention to? Is there anything to do against the spread of these alien earthworms? Why does Canada have so many more alien worms than the United States and Mexico?



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