There are all sorts of garden myths, but one of the strangest is certainly the one that suggests if you put out cornmeal, it will make ants explode.
According to this urban legend, when ants eat dry cornmeal, it will expand in contact with the liquids in their digestive system, creating so much pressure that they explode! A variant of the legend claims that ants die instead from flatulence. And yet another insists that it’s not cornmeal that you should feed ants if you want to kill them, but grits… or a mix of cornmeal and grits.
Obviously, this is all nonsense. Do you really think that the ants will start exploding like firecrackers because they ate something? In fact, cornmeal and grits make wonderful ant foods.
It’s easy to understand where this legend comes from. Commercial ant bait is often made up largely of cornmeal… not that cornmeal kills ants, but because they love it! It’s not the meal that kills them, but the insecticide that the producer mixed into it.
Worker ants can’t eat ant bait (i.e. cornmeal) because it’s a solid and they can only eat liquids. The queen ant too only eats liquids. So there is no danger they’ll eat the cornmeal bait themselves, then die of explosions or farting on their way back to the nest. Instead, they bring the poisoned meal back to their nest’s larvae and they can consume solids. They chew it up, partially digest it, then regurgitate the sweetened liquid that results from their digestion. This is the liquid the workers eat and that they feed to the queen.
If the larvae ate poisoned bait, one containing a weakly toxic product (usually boric acid is used), something that won’t kill them outright, and the queen eats it, she’ll be poisoned little by little and will eventually die. But only if the cornmeal contains a toxin.
It’s not the cornmeal that kills ant colonies, but the toxic product that is incorporated into it. If you simply apply cornmeal to the soil, as per the urban legend, you won’t be killing the ants, you’ll be feeding them.