Tom, if you want worms yo increase the worm population *in* the soil, ypu fon't want wigglers...they are perfect for vermivomposting to generate soil amendment, but won't survive in th Okanogan winter unlrss being warmed in a dung beap or compost pile.
They live on top of soil rather than in it.
Nightcrawlers burrow vertically down, living in the soil and eating it as well as vegetable matter.
Over time (years, not months) they will break up hard pan and clay.
The best way to incrrase their population is to practice good soil building practicrs. As you increase orgsnic matter in the soil and create attractive habitat they will come.
If you want to break up hard soil or clay, a green manure of forsge radish and winter rye will send roots deep in the soil, increase organic matter, and water/nutrient permeability, and maje a more attractive environment for nightcrawlers.