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native and non-native worm info

Page history last edited by PBworks 16 years, 3 months ago

 As a former vermicomposter, and a former worm-composting workshop teacher, I recommend that Wendie McClain think carefully about where these redworms will go after chewing up the leftover veggies. Most earthworms are not native to North America. I doubt there are any native earthworms in Hawai'i. In other North American ecosystems, such as the northwoods of Minnesota, introduced earthworms (deposited by anglers or vermicomposters) are destroying the ecosystem by eating the duff layer, which otherwise provides necessary thermal insulation for perennial native woodland plants (including infant trees), native insects, and other small animals, in winter. Though the plants in Hawai'i don't need protection from the cold in winter, they do need the highly transitory organic material in the soils. In tropical ecosystems, organic matter breaks down so quickly that the soil typically has very little organic matter, compared to the soils in temperate climates. Add worms to that system, and the decomposition may speed up even more, leaving nutrient-poor soils incapable of supporting native (or introduced) plants.

There may also be other problems currently unanticipated. For example, bacteria in the gut of earthworms have been shown to exchange genetic material. (My first worms came from a graduate student who was studying this.) Worms may introduce diseases or displace other native soil species. If there are no native species that have evolved to eat worms, they may expand their populations exponentially. Hawai'i already has so many problems caused by introduced species, I shudder to think of the problems introduced worms may cause!

If vermicomposters want to use the compost in their gardens or flowerbeds, or even in potted plants, the worms and their egg cases must be killed. The most usual method is by baking the compost at a high enough temperature to kill the eggs as well as the worms. Humans being what they are, however, someone will be sloppy and just dump the compost directly into their garden. As worms rarely stay where they're put, they'll escape into the ecosystem.

To read an article about forest damage by earthworms:

A New Angle on Earthworms, Author: Mortensen, Steve

Minnesota Conservation Volunteer Magazine, July-August 1998

To request a hard copy of this article, please send the name of the article, month and year of publication, and your mailing address to mcvarticles@dnr.state.mn.us.

Keywords: Forest management


more on non-native earthworms

Cworm Another very interesting paper [1] has come out on the impacts of non-native earthworms on forests, which I wrote about a year ago. As you recall, much of northern North America has no native earthworms, and microbes are primarily responsible for recycling leaf litter and thus controlling nutrient availability in northern forests. The rate of decomposition of leaf litter and nutrient cycling is crucial, because the forest floor is the physical foundation for all the native plants and trees of the forest community.

These communities evolved without earthworms.  European earthworms have been introduced into northern North America in large part through their use as fishing bait. Earthworms are detritivores, which means they eat and process this leaf litter, and have the ability to completely alter the physical, chemical, and biotic characteristics of the forest floor and upper soil horizons, notes the paper.

This study took place in Minnesota over four years, comparing vegetation in plots that had no earthworms to that in plots which had a suite of non-native earthworms.  Findings include:

    * As total earthworm biomass increased, density and abundance of herbaceous plants in half the study sites decreased, and the density and abundance of tree seedlings decreased in 75% of the study sites.

    * Regardless of biomass, sites with the most species of earthworms had the lowest plant diversity.

    * This could be due to a synergistic relationship between certain worms. Worms of the genus Aporrectodea did not appear to consume leaf litter until it was partly processed by other species.  Then they could quickly go about removing forest floor.

    * The species with the most impact was Lumbricus rubellus (often called redworms or red wigglers, and used not only as bait, but in vermicomposting). Where the biomass of L. rubellus was high, the herbaceous plant community was either absent or dominated by a common sedge and jack-in-the-pulpit.

The forest floor gets literally eaten out from under native plant communities.  Those with small seeds that can germinate on thin forest substrate (like Garlic Mustard) will have an advantage over native species with complex seed dormancy needs, and the root zones of plants that have chemical compounds that deter herbivory (such as jack-in-the-pulpit) are also sometimes avoided by worms.

In the conclusion, the authors stated:

    "Although local control of invasions may be possible in some situations, the magnitude and regional scale of earthworm invasions seem to suggest that in the next few decades a majority of hardwood forest will be impacted to some degree by earthworms."

It was mentioned that because of their disproportionate impact, introductions of L. rubellus should be prevented even in areas already infested by other species.  This is a species sold to people who use them to compost food and yard waste. These worms would eventually end up in the garden, so maybe it's a good idea, if you live in a northern state or province, to be careful about what type of worms you have.  There is a cool key to Canadian worms at WormWatch (or you can print this one out).

A fascinating -- and well-written -- paper.

[1] Hale, C.M., L. E. Frelich, and P.B. Reich.  2006.  Changes in hardwood forest understory plant communities in response to European earthworm invasions.  Ecology 87:1637-1649.

The right worm for the job

You may already be familiar with the ENDOGEIC worms that you dig up in your garden. These sub-surface dwellers, the earthworkers, promote healthy soil by creating tunnels that aid aeration, water penetration and water retention. They eat mineral soil along with bits of decaying matter and deposit their pile of castings on the surface. They live solitary, stable lives below the surface and are specialists in tilling the soil. Endogeic worms are NOT suitable for worm bins - leave them in your garden.

In contrast, composters are surface-dwelling or EPIGEIC worms, and their habitat is easily replicated in a worm bin. In nature, they eat decaying organic mater that falls on the surface of the soil, primarily animal manure. They have a high metabolism and live in dense colonies. They are specialists in waste management, processing their weight a day. Compostiing worms require a moist, nutrient-rich environment and in captivity will enthusiastically eat our household waste, including food scraps, cardboard, and paper. They reproduce prodigiously, and produce dark, rich castings called vermicast – a superb soil amendment and organic fertilizer.

Perionyx excavatus

Our composting worm in Hawaii is Perionyx excavatus, also called Indian blue, Malaysian blue, or blueworm. Although not native to Hawaii, they have been established here for a very long time and are commonly found wherever manure and water meet on pig farms, chicken farms and horse stables.

Perionyx excavatus is the worm of choice for tropical climates and is used extensively for vermicomposting in India, Cuba, Mexico and the Philippines.

Robust blueworms collected from local family farms may be purchased from Waikiki Worm Company, subject to availability. Click on the "Worm Shop" page for details.

Please do not import worms!

It is against the law to import worms from the mainland or other countries. The fine for importation is $25,000. Don't even think about it!

While the worms themselves cause no harm, they may carry in their gut the larva of an invasive species, the cluster fly. Local worms shipped interisland must be inspected and certified by the State of Hawaii Department of Agriculture.

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