Research plots have demonstrated that using grits does not control fire ants. The theory behind the use of grits as a fire ant control is that the ants will eat the grits, which swell in their stomachs causing them to explode.
However, this theory is incorrect because fire ant workers cannot eat solid food. The only members of the fire ant colony that can digest solid food are the oldest larvae (fourth instar), which turn all solid food into a liquid form for the rest of the colony to use.
This idea may have its origin in the fact that defatted corn grit is used as a carrier for most fire ant bait products. However, baits also contain various active ingredients (poisons) that control the fire ant colony.
Find more information about fire ants in eXtension's Imported Fire Ant Resource Area.