
Are Composting Worms, Such As Red Wigglers, Invasive?
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Definition of Invasive
From https://www.invasivespeciesinfo.gov;
As per Executive Order 13112 (Section 1. Definitions) an "invasive species" is a species that is: 1) non-native (or alien) to the ecosystem under consideration and, 2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health.
To be considered invasive, a species must fit BOTH of these requirements. Let's take a look to see if they both apply to composting worms.
Are Composting Worms Non-Native?
Red Wigglers (Eisenia Fetida) Native to Europe |
European Nightcrawlers (Eisenia Hortensis or Dendrobaena Veneta/Hortensis) Native to Europe |
Indian Blue Worms (Perionyx Excavatus) Native to Asia |
African Nightcrawler (Eudrilus Euginae) Native to Africa |
By definition, all composting worms, even red wigglers, are non-native to the U.S.
In fact, essentially all earthworms are non-native to America. But does this mean that they are invasive?
Do Red Wigglers Cause Environmental Harm?
To be qualified as invasive, the species must be non-native AND be likely to cause harm to their new environment.
For the last 20,000 years, most of North American forests grew without any earthworms, and the forest's plants have grown to rely on the deep layer of organic matter that sat on the soil surface.
The harm is done when this level of organic matter gets disturbed, or mixed into the rest of the soil. Earthworms do this as they consume the organic matter at the surface, then tunnel deeper, mixing the soil horizons together, and moving nutrients from the surface to deeper locations in the soil.
So, Do Red Wigglers Qualify as Invasive?
Since red wigglers are surface dwelling worms, meaning they stay in the O horizon of the soil, they don't "mix" together the soil like other earthworms. Although they are non-native, they don't pose a risk of harm to North American forests making Red Wigglers (Eisenia Fetida or Andrei) considered non-invasive.
Are other composting worm species invasive?
Other composting worm species, such as African Nightcrawlers and Indian Blue Worms also probably wouldn't be considered invasive as they are also surface dwelling worms. Additionally, they are tropical species of worms and likely wouldn't survive anywhere north of the Florida peninsula - which is most of the country.
European Nightcrawlers may be a different story. Some sources consider them an "epi-endogeic" species of worm, which means they are mostly surface dwellers, but have the potential to go deeper - which would harm north american forests.
If you don't live adjacent to a forest it will be fine to use european nightcrawlers for your composting or gardening efforts. If you feel there is a risk of them reaching forest soil, I would play it safe and avoid using that species.