yes, in most cases some or even all worm species are introduced .... minimal truth, interpreted to suit the leanings of the misinformed .... "red wrigglers" [E Fetida] are not much found "in the wild", as they require much higher organic inputs than is normally found in the field, so using them in a composting setup has no effect on anything other than the waste you feed them, also they're "surface feeders", not deep diggers like nightcrawlers - there are over 3000 species of earthworms in the world, not likely they were all "introduced invaders"

worms are found everywhere and not only DO NOT "use nutrients", but contribute to the sequestration of nutrients [including CO2] in a form that's MORE useful to plants - which is to say they convert decaying organic materials that may otherwise gas off nutrients [including CO2] into humic/mineral substances [heavily carbon based] that provide long lasting microbial food for later conversion by the microbes back into organic nutrients as the plants need/use them - my garden is extermely productive primarily brcause the growing medium is largely compost, worm castings, and worms

one of the single biggest eco-problems caused by human agricultural practices is the profiligate littering of the environment with rotting organic materials, particularly nitrogenous ones [like food waste], which in turn pollute our surroundings with nitrates, nitrites, and carbon dioxide ... proper composting and vermicomposting captures those nutrients in a fairly stable form [humus] for recycling usefully in the soil system

in some forested areas [mostly northern US], worms have had an effect on the regeneration patterns of vegetation, but I don't think it's been system-changing the way various invasive species of plants and weeds are, and the changes are mostly temporary

I'd ask'em if they have any knowledge of composting and particularly, nutrient cycles, or of the nature and function of the humus fraction of soils .... worms are part of the web of life in the soil, and contrary to what those folks probably believe, redworms don't eat dirt and leaves, they eat primarily microbial decomposerss, they're "carnivorous omnivores" just like us

about humus
about soil nitrogen
about soil and the biosphere carbon cycle

Bill

I think your friends may have heard an article on NPR - I think it was on All Things Considered. You might find it useful to do a search on he NPR web site to find out their sources...

BettyN

Thanks for the information, I listened to the NPR show, it was not very well presented, but they did mention a website which is much more concise

http://www.nrri.umn.edu/worms/default.htm

I knew that the worms we use for composting are not native. And I knew that before Europeans brought over non native worms, there were native worms here on the West Coast, and in agricultural areas such as Willamette valley, the natives are all gone, but some survive in the forests.
I guess the Eastern and Midwestern Forests are a whole different situation. The soil in these forests is being damaged by non native worms, primarily night crawlers that have spread by fishermen who use them as bait!!!
For everyone in urban areas utilizing compost worms , I am in Los Angeles, none of this really applies. But if you are lucky enough to be living and gardening in areas close to a real forest, please read more about why it is important not to contribute to the spread of non native worms into the wilderness.

Also , the food waste that I feed my worms , if I put it in the landfill, would create methane, a far worse byproduct than the co2 that the worms produce,so my worms are not adding to green house gases!!!

But I didn't think that my red wigglers would survive out in the back yard. So, I still feel okay about keeping them in a bin in the house.

It has made me wonder what I would do with them if I decided not to vermicompost (shock/horror!). But surely I could find someone to take them off my hands for me.