I never contemplated the huge differences between the different earthworm types, either. Apparently, my garden variety are ok, but there is a 'super earthworm', called a brown nosed composting worm. And, no, the 'Red Wigglers' you buy for fishing aren't suited at all to garden climates. Worms are best utilized in the compost bins, and in permanent plantings that you're not likely to rototill them into emulsion. Worms aerate the soil, and eat organic matter, turning it into 'castings', or manure.
Worms enjoy nothing more than wormy company.
They cluster in well, clusters, and if you have one happy earthworm, you probably have a whole colony mining your soil and fertilizing as they go. People who raise rabbits should not discount the benefits of a worm bed underneath the rabbit hutches. It's a symbiotic relationship that is hard to beat. Besides breaking down the urine and droppings, earthworms will also ingest the spent pelleted feeds and any dropped fresh groceries or roughage the rabbits spill. Occasionally, you'll want to use all this black gold the worms have created out of the rabbit bins.