When it comes to getting rid of pesty insects, old-spouses' tales swarm in as thick and fast as the insects themselves. You can find dozens, if not hundreds, of articles on the Internet touting cornmeal as a natural, effective and safe way to kill ants. What you won't find is any scientific support for the notion. Try it if you will, but you may have to add a little poison to the cornmeal to keep those ants from marching one by one, two by two, across your garden patio.
The Method Behind the Myth
This is the story you will read on the Internet about how cornmeal purportedly kills ants: Ants like to eat cornmeal and, if you spread it across the paths they regularly take in your home or garden, they will eat it. Since ants can't digest cornmeal, it swells inside their digestive tracts when they drink water, killing them.
Although the idea doesn't seem inconceivable, it is something that could be easily proved by scientific research. Given the dearth of scientific support for this system of ant-control, it seems unlikely to be effective. On the other hand, you won't endanger your kids or pets by trying this.
Baiting With Cornmeal
Although perhaps of shaky effectiveness as an ant-killer on its own, cornmeal can get the job done when used as part of a baiting system. Ant baits combine a food ants like to eat with a pesticide. Experts at the University of Colorado Extension suggest that use of ant baits provides the most satisfactory control of these insects.
You can buy ant bait, but it is also possible to make one yourself with cornmeal.
Add 9 parts cornmeal to 1 part insecticide like boric acid or borax. Bait insecticides must be slow-acting so that the ant finding the bait doesn't die before it carries the bait back to the nest. Add sufficient soybean oil to make the mixture into a paste.
Place the cornmeal bait in a sealed container with punched entry holes. Place the containers out away from areas frequented by children and pets. It is poison if ingested and can also be toxic on repeated exposure.
Clean your house and yard to make sure that the ants do not have any other source of food. Fix leaks in pipes and faucets to eliminate other sources of water.
Check every few days to see if the ants are eating the bait. Different foods are acceptable to different types of ants, so if the cornmeal/soybean oil doesn't appeal to them, try something sweet , like honey, or something greasy, like peanut butter.