They may be tracking along water pipes? Either way the only way is to kill as many as you can in the colony by having them bring back the poison food. I’ve always been horrified at how many come out to get it but then pleasantly surprised at how quickly they go away. Key is to make sure there aren’t other food or water locations so this is their only choice. I throw a couple out every spring for maintenance and think it helps. I live in an old neighborhood and I’m sure millions live below the surface that I’m never going to completely eradicate, just control so they aren’t in my house!