. . they're a bit scarce around here right now, the drought and heat have apparently taken their toll.

Fish will bring them in faster than anything else. When I do get an invasion, I find the entry point and give it just a tiny spritz of unscented Black Flag. Then I use my industrial heat gun, set to high temperature and low air flow, and roast all that are in the trail. They are remarkably poor at finding another entrance once the one they were using has been poisoned.