my father used to pour water on the ground. Then he would take an electrical cord with a metal rod on each wire and stick the rods in the ground a couple of feet apart and plug it in. Not too safe, but it seemed to work. I stick to picking night crawlers by flashlight myself, or just dig them from the garden if I want smaller ones.
Other people asked questions on similar topics, check out the answers they received:
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them