My vermicomposting adventures have made me realize how fast composting worms can populate. I’ve watched with amazement as the number of red wigglers has grown in my worm bin, so much so that I even began wondering if worms could serve as a food source if we ever faced a global famine. But I also wondered if there was any threat of them becoming invasive since they are not native to North America.
Are composting worms invasive? Composting worms are not considered invasive at this time due to causing no known harm and having natural prey to keep their populations in balance. Because of their resilience and remarkable ability to populate, however, there is a risk that compost worms could become invasive in the future.
What Makes A Species Invasive?
The term invasive generally means that a species, whether plant or animal, competes for food, living environment, or other essentials to life at a rate that inhibits the natural flourishing of the native species. In extreme cases, an invasive species may cause a detrimental impact on the environment where it lives.
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In short, an invasive species:
- Is not-native to the area
- Causes Harm
In order for a species to become invasive, it has to be able to adapt to the change in environmental conditions (temperatures, food sources, etc.) where it is transplanted. Assuming it is able to adapt to the environment, the tendency to populate and consume in excess is what usually results in harm to the ecosystem.
According to Environmental Science, a lack of predators is a key issue with invasiveness. Nature has a way of keeping things in balance. Over time, predators and prey are established to maintain population balance. When a species is removed from its natural habitat and relocated to an area where it does not have natural prey, it can result in extreme overpopulation of the species.
As a result of this overpopulation, invasive species can consume the natural resources in their environment, potentially starving other native species into extinction (source).
A search for red wigglers under their official name, Eisenia foetida, yields no relevant results on invasive.org, a website that catalogs invasive species of plants, insects, and animals that stand to pose harm in North America (source). Similarly, a review of the US Department of Agriculture’s National Invasive Species Information Center website does not show red wiggler worms in the list of known invasive terrestrial invertebrates.
This short video from National Geographic outlines the impact of various types of invasive species and how they harm the environment of non-native territories.
The Potential For Red Worms To Become Invasive
Let’s look at red wigglers against these criteria and consider their potential to become an invasive species.
First, compost worms have demonstrated an ability to reproduce at an impressive rate. When provided with optimum conditions, they can quickly reach population capacity within a worm bin and begin suffering from limited food resources. A common sign of this is having large numbers of small worms compared to larger ones.
Next is the tendency to consume in excess. In the case of red worms, they are sought out specifically for this ability. This is a species that can consume roughly half their weight in food daily. This need has been theorized to motivate composting worms to relocate their populations in search of new food sources. It is, in fact, one of the most common reasons that red wigglers will attempt to escape from their compost bin.
Regarding its native origin, the red wiggler compost worm is not native to North America. It was transported from European areas and has been transported to many continents across the globe (source). This ability to adapt to different environments demonstrates a level of resilience by red wigglers.
However, compost worms have not demonstrated cold tolerance that scientists believe to be essential to thriving in an invasive manner. A study published in the American Midland Naturalist found evidence that red wiggler eggs did not survive well in winter conditions, limiting the likelihood of the species becoming invasive (source).
Another factor that inhibits the invasiveness of red worms is natural prey. In addition to toads, lizards, and many ground-crawling insects that eat worms, humans have taken to using red wigglers as fishing worms. The abundance of natural prey limits the composting worm’s likelihood of becoming invasive.
Finally, the one factor that is as of yet unknown is their ability to do harm to the ecosystem. I have read studies where it was suspected that their tendency to populate and consume in excess could result in limited resources for other species. However, a larger population would be likely to bring natural prey which would help to keep their populations under control. And this is the key to a balanced ecosystem.
Note: I recently received an email from a reader in Rhode Island who explained that she is seeing evidence of invasive nature of compost worms. Her insights are worth reading.
Responsible Management Of Compost Worms
Though not considered invasive at present, the potential for compost worms to become an invasive species does exist based on their ability to adapt and their tendency to populate and consume in mass. Worm bin farmers are discouraged from releasing composting worms into the wild.
Invasive issues aside, composting worms provide an excellent method of dealing with discarded food scraps. While we often think of this as a backyard hobby, worm farming can be put to use on a massive scale to offset landfill waste of kitchen scraps.
- An airport in North Carolina, for example, composts leftover food from travelers using almost 2 million red wiggler worms (source).
- Vermicomposting has even been tested with favorable results as a solution for manure management (source) and in fact, has significant advantages over manure as a natural fertilizer.
Compost worms pose the potential to be invasive due to their tendency to reproduce and consume in excess. The primary impact potential that these worms have as an invasive species lies in their potential to deplete a food source that other species depend on to survive. Given the abundance of natural prey, however, along with an inability to thrive in colder conditions, it is unlikely that they will pose a threat to an ecosystem where they are transplanted. Responsible management of red wigglers is recommended to lessen the likelihood of invasive behaviors in local areas.
So if you are worried that your compost worm farm is going to wreak havoc on the ecosystem, you can likely take a deep breath and relax. So long as you are managing your worms in a responsible way and providing them an environment where they can thrive, they should be of no threat to the environment and in fact are making valuable contributions to the quality of your soil while keeping landfill waste down.
Vermicomposting is an excellent solution for indoor composting. If you are living in an apartment or just don’t want to deal with the hassle of managing an active compost pile outdoors, consider the advantages of composting with worms.
Click here to see our recommended composting products including indoor worm bins.
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