While growing up we never bought earthworms for fishing, we harvested them ourselves late at night using a homemade electrical prod. The device we used I do not recommend using without using extreme caution as this is not an approved device and could get you shocked if not careful. Make sure that the extension cord you use is either brand new or carefully inspected for cracks or deteriation, don't use a cord that is junk ruin a perfectly good extension cord, LOL! Next item to disassemble and ruin is a bicycle pump, preferably one that is broken but it doesn't matter, it will soon be broke anyway. What we are after is the plastic handle and metal rod it's attached to. The handle needs to be made of something that doesn't conduct electrictricity, you'll be holding on to that soon enough. Once the handle and rod are removed from the bicycle pump, remove the piston from the bottom, discard the rest of pump it's useless. Cut the female end off the eletrical cord and strip back a few inches of insulation from both wires of electrical cord. Wrap each end of wire seperate from one another onto the metal rod from pump. Tap each connection with lots of electrical tape or other means. Plug device into electrical outlet late at night into rabbit droppings and should produce plenty of earthworms. Sometimes we would add water for a few days if it had been dry lately. I never bought any earthworms growing up for fishing. Please use extreme caution using this device, it can electricute you if not careful. It's my understanding that if might be a little safer if you were to use a transformer or rheostat to control the voltage somewhat if one is hesistant to make one of these. We never had a problem while using ours but hey it was long ago and things are different now. I tried to find a picture online but was unsuccessful, maybe I'll have better luck when I have more time to research or make another myself. Hope this helps!
We used to catch them by hand. Soak the ground (and I do mean soak it) in the afternoon and go out after dark with a flashlight. They'll be lying on the ground with one end still in the hole they came out of. Anyone that things those buggers are slow is in for an awakening if you don't sneak up on them carefully.
Grandpa's was similar to yours, CC, except he just took a long, sturdy, metal rod and bent it into a "T", then put some insulated handles (like on a bicycle) at the top. Ahhhh... the good old days; when near electrocution was a family event .