A common question I receive is " How many worms should I get for my raised beds" The problem with this question is that there are 3 different types of earthworms: Anecic, Endogeic, and Epigeic.
Anecic are your nightcrawlers you find in the ground. They live in the soil and have vertical burrows. They also eat soil and litter ie compost. Alabama Jumpers are a common commercial raised anecic worm. Disclaimer: Alabama Jumpers might destroy forest due to their rapid eating.
http://www.scientificamerican.com/article/invasive-earthworms-denude-forests/
Endogeic live in the soil in horizontal burrows and just eat soil and you never see them on top of the ground and only see them when you dig in the soil.
Epigeic live in litter ie compost with no borrows and eat compost. Most commercial raised compost worms are this type: Red Wigglers, European Night Crawlers and African Night Crawlers.
People want to put earthworms in their raised beds for aeration but the same thing can be done with the use of worm castings. Instead of putting worms into raise beds it might be best to have an indoor worm compost bin and use the castings in the beds in the spring and fall. The other benefit is that you don't have to buy worms every spring due to a lose in the winter and outside creatures eating them.
