here's an interesting definition I found for piss ants under "pests"...
Pissants, Piss Ants
Odorous Ants, Piss Ants, Sugar Ants
In the United States, any small or tiny ant that infests a home is often labeled as a Pissant or piss ant. An actual Pissant is an ant that lives in certain European forests and gets its name from the odor produce by its nesting material - pine straw and pine needles. Middle English pissemyre : pisse, urine (from the smell of the formic acid that ants secrete); piss + mire, ant (probably of Scandinavian origin; akin to Danish myre).