Effective. This is one of the simplest ways of dealing with one or two problem colonies. Basically, the procedure is to rapidly dig the mound and a foot or so of soil under the mound and dump it into one or several large buckets. Sprinkling the bucket and shovel with baby powder or cornstarch before you starts keeps the ants from climbing out of them. Remember to tuck your pants into your socks to keep the ants where you can see them.
Dig up the soil at a time of day when most of the colony is in the mound. In the spring, the best time is usually mid- to late morning. In the summer, it might be early morning.
Once the ants are in the bucket, you can choose to drown the ants or simply to carry them to some place where they are not a problem. If you choose to drown the ants, add a generous squirt of dish soap, water from a hose, and stir to mix the soap throughout the mud in the bucket. The soap breaks the surface tension and drowns the ants much more quickly. It usually takes overnight to kill the ants. In the heat of the summer, they will probably drown faster, but on cool days in the spring, it may take longer. It is best not to fill the buckets more than three-quarters full of ants and dirt so there is room to add the water.
Related: A Safe, Effective Ant Trap
Effective.Pouring hot water on the mounds is effective and environmentally friendly, but may require 3 or 4 applications to kill the colony. Water should be at least scalding hot, but does not need to be boiling. This works best when you use 3 to 4 gallons of water in each application. WARNING: Hot water kills grass and shrubbery and may cause severe burns if spilled onto skin.
Ineffective. The theory is that the fire ants will eat the dry corn grits, drink some water, and then die as the corn grits expand inside them. The image of greedy little ants exploding like popcorn inside their mounds is very compelling, but the problem is that fire ant workers only drink liquids; they are incapable of ingesting solids. Fire ant larvae will eat solid food, but they chew it up and mix it with saliva just like we do before they swallow it. Grits simply don't work, so any perceived effects are due to mound disturbance and colony movement.
Ineffective. This is similar in theory to corn grits.
Effective. Little crystals of silica are supposed to scratch the ant's cuticle so they dehydrate and die. Indeed, if you take a colony of ants and shake them up in bag with diatomaceous earth, about half die. But when you use it on ants outside they usually find ways to avoid it so not many ants are killed. They will not eat it in food and foraging ants do not track it into colonies where it might kill the queen or young fire ants.
Ineffective. The idea is that workers from the two colonies fight until they kill each other. While workers from two single-queen colonies will fight if they are mixed, it will rarely result in both or even one colony being killed. And if you mix fire ant colonies together with multiple-queens in them, it only makes for a bigger party.
Related: Got Ants? A Natural Solution
Straw Itch Mites
Mixed. Some studies have shown moderate benefits from releasing these beneficial mites, but other studies have found none. However, the most dramatic effect has been the large rashes that researchers have gotten from some of the stray mites that they were releasing. Oops!
Mixed. As in "place ant in the middle of block A and then rapidly apply block B." Very effective on an ant by ant basis, but a lot of work for a colony with a quarter million workers!
DO NOT USE! It is dangerous to the environment and to your health to pour gasoline onto the mounds. Extensive or frequent use can threaten the purity of your ground water. Igniting the gasoline intentionally or accidentally does nothing to improve its effectiveness, but it can pose a serious threat to your health and property.
Household Cleaning Products
Ineffective. Most don't work at all. Some act as a repellent, causing the colony to build new mound a few feet away. Anything that does work is likely to be expensive and bad for you, your yard, and the environment.
Ineffective. Exhaust fumes from a car or riding lawn mower can be pumped into fire ant mounds. About 12 years ago, I tried it with my old VW Superbeetle. After about 15 minutes the result was that most of the ants were motionless, but 30 minutes later, they woke up and went back to work. Maybe 30 to 40 minutes of exhaust fumes would be effective, but that is a long time and I hear that plugging up the exhaust systems of gasoline engines can be pretty hard on them. (Fortunately, my VW still worked, but so did the ants.)
Mixed. Mechanical devices that cut, chop, stir, mix, pound, or grind up fire ants in their mound can be effective during times of the year when most of the colony is up in their mound. The benefit of these devices is that they leave no chemical residue. The problem with them is that they are usually expensive to purchase, labor intensive to use, and inefficient in dealing with colonies under rocks, roads, sidewalks, or shrubbery.
Effective. These can work well, but like hot water they will kill grass and shrubbery. Also see comments about mechanical devices.
Ineffective. I don't know of any that work. With the one I tested, fire ants moved in and built a mound around it after about a month when the weather turned cold and the vibrating rod was nice and warm.
Electric Bug Zapper Grids
Ineffective. These dramatically kill ants that run across them—the problem is that all fire ants are not like lemmings. A large majority of the colony runs the other way while only a few stay and "fight" the zapper.
Mixed. Contrary to what their name implies, giant ant eaters in South America do not eat ants. They eat termites. Besides who would want a 200 pound animal with claws and arms as strong as a bear wandering through their neighborhood! Our little native ant eater, the armadillo can be enough of a problem.