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.) 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.
A search for red wigglers under their official name, Eugenia fetid, 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). 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.
When provided with optimum conditions, they can quickly reach population capacity within a worm bin and begin suffering from limited food resources. 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). 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.
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). Compost worms pose the potential to be invasive due to their tendency to reproduce and consume in excess.
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. This guide will introduce you to the red wiggler to include a deeper on dive on the species and information on breeding, life cycle, and reproduction.
Native to Europe, arena fetid are not classified as invasive species in North America as they are not considered to have a negative environmental impact in the wild. This species features a vibrant color with yellow banding and is closely related to the more uniformly-pigmented arena Andrei.
A study suggests that the two can produce hybrid offspring, a phenomenon which should otherwise be considered impossible between most worm species. Fun fact: The “fetid” part of the binomial name refers to what some say is a foul-smelling secretion the red wiggler uses to fend off predators.
The anatomy of a red wiggler resembles that of other common earthworms; a long-segmented body begins at the pointed head and terminates at a slightly-flatted tail. A fleshy band called a flagellum features prominently on the body of the red wiggler at roughly 1/3rd of the length of the worm.
The digestive tract is simple, starting at the mouth where the worm begins to consume its food before passing it on to the pharynx. Calciferous glands in the stomach also serve to neutralize acidic foods passing through the worm's digestive tract.
The intestine forms the longest part of the worm and is where the majority of digestion takes place via enzymatic processes. The castings eventually pass through the anus at the end of the worm as capsules coated with a biologically-rich mucus.
Red wigglers, like all earthworms, are hermaphroditic, simultaneously possessing both male and female sex organs, both of which are used in the reproduction process. Two worms of the same species will intertwine around each other's criteria, secreting sperm through their skin, eventually producing a cocoon.
If you're curious how quickly red wigglers can reproduce, check out the Urban Worm Calculator. The mighty red wiggler may be used as a bait worm for smaller fish or as a protein source for chickens and reptiles.
Rather, a combination of cost, hardiness, and comfort in a wide range of temperatures makes it the most appropriate composting worm for most new vermicomposters Red wigglers are a resilient composting worm, tolerant of a wider range of temperature than other species.
For instance, its larger cousin, the European Nightcrawler prefers cooler temperatures in the high-60 °F range. The red wiggler can tolerate both the low and high ends of these ranges, reproducing and processing organic waste well between 55 °F-90 °F.
Its cocoons are famously hardy as well, able to withstand prolonged freezing temperatures, staying viable in a suspended state until they are able to hatch in warmer weather. But red wigglers are nobody's idea of cheap, and the skyrocketing demand for all things garden-related due to the COVID-19 pandemic of 2020 boosted prices of all composting worms.
This reduces weight, but more importantly, the risk of microbial activity raising the temperatures to deadly levels while the worms are in transit. So make sure that your postman is directed to leave your shipment in a shaded, protected environment if you won't be home to receive your worms.
But if you're ordering from PetS mart, PERCO, Walmart, or another large company that is not directly related to the vermicomposting world, be careful! To save on shipping cost, you may want to see if there are any nearby “Mom and Pop” stores through a Google search.
With the appropriate temperature, moisture, pH, and food sources as discussed below, you should achieve higher densities, perhaps 2-3 lbs per square foot or so. This prevents a mucky, muddy vermicompost that will be simply difficult to harvest at best, and a stinky, anaerobic mess at worst.
The European Nightcrawler, the larger cousin of the red wiggler, is just as voracious and also makes for a good bait worm. The African Nightcrawler is a very large composting worm and makes a beautiful, granular cast.
The Indian Blue is voracious, but also prefers a warmer climate, and it also exhibits a tendency to escape the bin. I like to call it the Ford Taurus of vermicomposting worms ; you won't brag to your hardcore composting buddies that you own them, but they will serve you well.
Even if they did, the glaciers killed any native North American earthworms in our region. There are over 100 species of native North American earthworms in glaciated areas such as the southeastern U.S. and the Pacific Northwest.
However, native species have either been too slow to move northwards on their own or they are not able to survive Minnesota's harsh climate. More recently, the widespread use of earthworms as fishing bait has spread them to more remote areas of the state.
Without worms, fallen leaves decompose slowly, creating a spongy layer of organic “duff.” This duff layer is the natural growing environment for native woodland wildflowers.
Invading earthworms eat the leaves that create the duff layer and are capable of eliminating it completely. Big trees survive, but many young seedlings perish, along with many ferns and wildflowers.
In areas heavily infested by earthworms, soil erosion and leaching of nutrients may reduce the productivity of forests and ultimately degrade fish habitat. They also help incorporate organic matter into the mineral soil to make more nutrients available to plants.
For instance, their castings (worm excrement) can increase erosion along irrigation ditches. Most of our native hardwood forest tree seedlings, wildflowers, and ferns grow best in these conditions.
Less infiltration combined with the removal of the duff and fallen tree leaves results in increased surface runoff and erosion. If we stop introducing them we can retain earthworm free areas for a long time.
Jumping earthworms (also known as Months worms) are a new species starting to spread in the Great Lakes states. However, if they or other species are able to survive winter and escape from compost piles they could further harm native forests.
See the brochure A B C's of Composting with Earthworms Safely by Great Lakes Worm Watch for more info. It's illegal to release most exotic species into the wild (Minnesota Statutes 84D.06).