If you leave them long enough, they will form a trail. The random ones are scouts. Once you see the trail, follow them back to find out where they're coming from. No use picking them up or trying to break their trails as they follow an exact path marked down by the scouts. Just leave the scouts to do their thing. They'll find the bait eventually.
My mum in Nelson had them really bad a few years ago. One day I managed to collect 2 ice cream containers of raining ants with the help of 2 big cans of fly spray.
If you have kids around and see them outside on concrete, a fun trick is to get some thick chalk and draw a circle around them. The ants won't cross it and will just stay running around in the circle for hours, or until one of them builds up enough courage to just go for it.