Small indoor pest ants that can be controlled with boric acid and sugar. Use baits containing apple mint jelly and a small amount of boric acid. Powered cinnamon is an excellent repellent.
Here is my take on why grits or cornmeal can inhibit Ants.
Fire Ants vary their diet seasonly. Typically they go after proteins more in the Summer(worms or dead bugs or meats or animal oils, etc.). In the Fall and Winter, they diet more on carbohydrates. This is when starches (grains) are more appealing to their diet.
Probably what makes the cornmeal (or the cornmeal nature of grits) more effective in inhibiting Fire Ants is that they feed this to substance to their larvae in order to break it down into a digestible food source for the adult Fire Ants. Their food source normally is based upon a type of fungal breakdown in concert with their young. This is inhibited by the cornmeal. The antifungal nature of the cornmeal/grits upsets this feeding cycle where the adults can not obtain their final food product (a fungus-based food secreted via the larvae). Essentially, the Fire Ants start to starve because their primary food source isn't happening -- it has been "infected" as a result of the antifungal activities of the grits or cornmeal.
Some of the details of this cycle might be rough around the edges on my rendition, but this is probably why people find success with grits this time of year. In the summer, grits will probably be less effective.
I am no Scientist, but I do a lot of research alon with experimentation in the real world.