They usually appear early evening when it has been raining, I tend to have a more humane method. Use one of those large plastic dishes you have bought something in the supermarket in, like meat or fish, scoop them up with a garden trowel, and dump the whole dish in the garden of one of the neighbours who you don't like .. as far away as possible without being seen, preferably under cover of darkness. They won't find their way back. I have scooped up 50 on a good night, and next morning the dish is empty.