This has piqued my interest!
Here are some tips for ecologically friendly vermiculture:
What's in My Worm Bin?
With invasive earthworms wriggling amok in our forest soils, gardeners who use worms to decompose kitchen scraps and plant waste may want to take a closer look at what they’ve got growing in their compost piles. Some of the traits that make worms ideal for vermicomposting—such as high reproductive rate and adaptability—may also make them potentially successful invaders.
The worm predominantly sold for composting is the red wiggler or red tiger worm, Eisenia fetida. It has a rusty brown color with alternating yellow and maroon bands down the length of its body; a pigmentless membrane separates each segment. It grows up to three inches long and is highly prolific. Though the worm has established itself in the wild here, so far it has not been identified as a problem species.
Another popular compost species, the red worm, Lumbricus rubellus, is causing trouble, however, and should be avoided. It also grows up to three inches long and has a history of being confused with E. fetida. This worm is dark red to maroon, has a light yellow underside, and lacks striping between segments.
In The Earth Moved (Algonquin Books, 2004), a wonderful new book on earthworms by Amy Stewart, forest ecologist Cindy Hale advises worm composters to freeze their castings in air-tight bags for a least a week before adding them to garden soil, no matter what worms species they use. "It won't hurt the soil microbes, but it will kill all the worms."