Before you do anything to trap/kill them, fix the problem. Then you'll only be left with the existing ones. Sticky traps are beyond inhumane, go with snap traps or electric ones. There are some electric ones that will capture like 10+ at once.
Semi cruel, a bucket of water with a wire going accross and put blueberries or other floating food in the water. They'll go on the wire, fall in and drown. Still less cruel than the glue traps though.
If there's only a few, cheap snap traps are the way to go.