In California, we periodically have problems with armies of Argentine ants invading houses at certain times of the year.  It doesn't matter how clean you keep your house or how carefully you maintain it, they'll still find a way in.  They're quite small and routinely squeeze through cracks less than 1mm in size, which is roughly the size of the gap between a baseboard and floor in most homes out here.  They invade (and I use that word carefully) in extremely large numbers, often in the hundreds; often your first sign is an inch-wide column of ants marching down a …