There are six known species of fire ants in the United States. They are called fire ants because they inflict painful, venomous stings. Four species are native, and two came from South America. The red imported fire ant (Solenopsis invicta) has inhabited the southern United States since the 1930’s, but in recent decades has been moving northward and across the southwest. The black imported fire ant (Solenopsis richteri) has been found in Texas, Mississippi, Alabama, and Tennessee since 1918, but its range is limited because of less tolerance to colder weather. Imported and native fire ants are similar in size and appearance. They are reddish-brown or black in color and measure up to a quarter inch long. They also exhibit basically the same behavior when threatened. Fire ants, when disturbed, swarm toward AND crawl onto an invader. Once in battle mode, fire ant workers bite with their mandibles and can sting multiple times with stingers attached under their abdomens at the same time.
I really want to talk about red imported fire ants. Two things make them of greater concern than their native cousins. First, they are more aggressive. Both types swarm…but imported ants charge straight up vertical surfaces such as walls, blades of grass, animal or human legs! You can tentatively check what kind of species you have, by sticking a pencil in a mound and seeing if they climb vertically. Second, imported ants are more numerous and their colony size is overall larger. Unlike native species, which are part of the balanced ecosystem, red imported ants have few natural predators in the United States. This has enabled then to grow, flourish and move over a wide range, sometimes displacing native fire ants.
As far as natural predators go, man is about it. There is one other that is promising…a biological control parasite called Pseudacteon crawfofdi (the Phorid fly). These parasites have been used in experimental capacities with some success. How do they work? They dart in long enough to lay an egg on a worker and then fly off. A larva hatches, enters the ant’s body, consumes the insides, and then emerges as an adult. Fire ants are very hard, if not impossible to eradicate. Knowing about their biology may prove to help conquer these foreign invaders. Red imported fire ants create nests that look like mounds of loose soil with no central opening. They also like to build inside barns and structures, and tend to like electricity switch boxes, breaker boxes, or light housings also. When you come upon a mound in question, observe it for a few minutes. Do you see worker ants of different sizes from 1/8 to ¼ inch in size? You probably are looking at red imported fire ants; species of other ants tend to be more uniform in size. Their swarming and stinging behavior, the resulting pustule that arises and itches from being bitten, is what sets them apart from other species. The swarming activity that they exhibit, makes it very likely that an animal or human will receive multiple bites. Animals, especially horses, cows and humans can be covered in hundreds of ants before the signal is given through pheromones to sting. Ants communicate primarily via pheromones, which are similar to hormones, but are emitted through the air. They coordinate their attacks to intensify more injury to their victims. One of those communication agents is the “alarm pheromone”. A chemical warfare agent that drives the ants into a frenzy of stinging. If only one ant releases the alarm, then hundreds or thousands of ants will start stinging suddenly. Many mounds contain 100,000 ants!
There has been some recent documentation about hybridization of ants between native fire ants and some of the more rare venomous South American strains. Some species in South America can kill a human with one bite. Some incidents of fire ant bites have resulted in allergic reactions, sepsis and other severe conditions in a few individuals. There is speculation about whether these hybrid ants are here in the United States, and are able to inflict potentially harmful bites. Especially if the bite area is in direct contact via the vein and bloodstream of an animal or human.
What should we do to eradicate them? The secret is to exploit their weakness: a colony’s communal stomach. Ants are divided into foragers, workers, and nursery workers who tend to the queen and her brood. Foraging ants do not simply bring food back to the queen and her brood. Instead, the foragers eat the food in the field and partly digest it before regurgitating it into mouths of workers. Then workers regurgitate the food and feed it to the nursery workers who swallow it and digest it further. They then feed it to the queen and her brood. This is a process called “trophylaxis” and protects the queen from poisoning through multiple layers of “testers”. That’s why a slow-acting poison that spreads throughout the whole colony before having any toxic effects can eliminate the entire population.
Chemical baits that works as a slow-acting poison are called Hydramethynlon (trade names Amdro, Max Force, and others). Other slow-acting poisons are Spinosad (Green Light Ant control), and Pyriproxyfen (Spectracide Fire Ant bait), Baits will not poison mammals. It can be deadly for chickens and other poultry if they eat it. It is toxic to fish also. Baits (powder of granules) are sprinkled on or around the mound. Hydramethylnon works as a metabolic inhibitor by blocking the biological process in the ant that makes ATP (adenosine Triphosplate). ATP is a compound required by most biological processes to provide energy for life. Without ATP, the ant becomes lethargic and stops eating causing death. The feeding process of the whole colony is stopped. The EPA has classified Hydramethylnon as a “group C possible human carcinogen”, so use with care.
A drench or dry treatment using liquid chemicals (mound application) can be used also for effective quick kill applications when ants pose imminent danger to people and animals. Some products used for this include Deltamethrin (Bengal UltraDust), Permethrin (Real-Kill fire Ant killer), and Acephate (Ortho orthene fire Ant Killer).
Organic fire ant control uses these products: D-limonene (Citrex), and Pyrethrins (Organic Solutions).
Other natural methods include diatomaceous earth and a method of coating the mound with baking soda and then pouring 20% vinegar on it, causing a chemical reaction and quick kill.
Please remember that they swarm, and be careful around the mounds.
Texas Agri-Life extension services
Claborn, David DrPH
Kidd, Hetal.1991The Agrochemicals Handbook. Third edition. Royal Society of Chemistry Information Services, Cambridge UK pps.10-12Taber, Stephen Welton Texas A&M University Agriculture SeriesUnderstanding Fire Ants: How to Identify and Control Them