Well if you want to catch a few in a short period of time, do it by hand. Look under rocks, and once you see one, put one hand behind it. Then startle it from the front so it shoots back into your hand.
Now if you want to catch a ton over a long period of time, use a trap. You can buy one, or make one > http://www.ehow.com/how_12069613_make-ho... Just find a good spot, put a hunk of hotdog or dead fish in there, and wait a few hours.
