What are red imported fire ants? What makes them different from Texas native ants?

Red imported fire ants or Solenopsis invicta are medium-sized red and black colored ants that build mounds of soft soil. Mounds are rarely larger than 18″ in diameter. In cold, dry areas such as the High Plains of Texas, mounds are usually much smaller and harder to detect. When disturbed, fire ants emerge aggressively, crawling up vertical surfaces, biting and stinging “all at once”. Their sting usually leaves a white pustule on the skin. Worker fire ants vary in size from small (1/16 inch) to large (almost ¼ inch) in length. Many native ant species have worker ants that are uniform in size and may vary in body color. Other small to medium-sized ants that build small nests in soil often have central nest openings through which the ants enter and leave whereas fire ants mounds have no central openings.

Harvester ants are much larger and make large bare areas with a single entrance hole to the colony.

Leafcutter ants are also much larger and have a distinctive built-up dense cluster of mounds at the colony’s center called a “town”, and have many entrance holes over a very large area.

Can I tell the difference between fire ants and native ants? How large are fire ants?

Some uncertainty comes from the fact that red imported fire ants vary in size (1/16 to almost 1/4 inch long – see image by S. D. Porter, USDA-ARS), with the largest workers 2 or 3 times larger than the smallest. Red imported fire ants are an exotic invasive species and in many areas of Texas they have displaced other species of fire ants native to the state.  Solenopsis geminata, the tropical fire ant, is the most common native fire ant species encountered. To the unaided eye, they are almost identical to red imported fire ants. However, S. geminata will have a few larger workers with large, square-shaped bi-lobed heads. These ants specialize in collecting and milling seeds, but build mounds similar to red imported fire ants.

What is the difference between single queen and multiple queen forms of the red imported fire ant?
There are two genetically distinct forms or the red imported fire ant, Solenopsis invicta: The single queen or monogyne form and the multiple queen or polygyne form.

Single queen (monogyne form): only one queen (reproductively active wingless female) per colony or mound; slightly larger worker ants; members of colonies are territorial; mounds generally larger in size; mound densities usually less than 300 mounds per acre; fewer ants per acre.

Multiple queen (polygyne form): more than one and up to hundreds of unrelated queens per colony; smaller average worker ants; worker ants move freely from one mound to another and share resources; mound densities greater than 300 mound per acre; more ants per acre.

How can I tell the difference between fire ants and termites?
Although most ants are recognizable, some forms of winged ants are often confused with termites, especially during the termite swarming season. The front pair of wings on ants is larger than the hind pair, while the four wings of termites are approximately the same size. Ants have “elbowed” antennae and a “thin waist” (narrow between the thorax and first abdominal segments). In termites, the thorax and abdomen are broadly connected and their antennae are straight and hair-like.

What are carpenter ants and how do I control them?
Carpenter ants are usually larger than most other house-infesting ants. They vary in color from a dull black or reddish yellow color to a combination of black and dull red or reddish orange. Worker ants range in size from 5/16 to 7/16 inches long. Carpenter ants tunnel into wood to form nest galleries. If they go unnoticed for several years, some species of carpenter ants may cause significant structural damage. In Texas, carpenter ant species are more of a nuisance when they forage indoors, often attracted to sweet foods. Species may nest in almost any crack and crevice and often occur in structural wood where water leaks or rot occurs. Outdoors, the ants use dead trees or tree limbs, stumps, logs or areas under stones as nesting sites. Once the carpenter ant nest has been located, control is relatively easy. Nests can also be removed and infested wood replaced, if feasible. Treatment options include use of a bait or residual contact insecticide applied as a dust or spray to the nest. It may be necessary to drill small holes in wall voids, baseboards, window and door sills to apply insecticides to the nest or major part of the colony, procedures best done by a professional pest management provider. Read and follow the product label for best results.

For more information, read Texas Pest Ant Identification: an Illustrated “Key” (010) [PDF]

Where do fire ants come from?
Red and black imported fire ants (Solenopsis invicta, and S. richteri) are native to South America. They were accidentally introduced into  the U.S. around the 1930’s through the port of Mobile, Alabama; probably in soil used for ships’ ballasts  and have been spreading since. There are several Solenopsis fire ant species native to the U.S.

We didn’t used to have fire ants when I was a kid. Why do we have them now?
Red imported fire ants are a very aggressive, efficient competitor ant species. Since the 1950’s in Texas, the ant has been spreading north, west and south. They now infest the more than the eastern two-thirds of the state, and some urban areas in western Texas. The bad news is that they are probably here to stay. The good news is that, with relatively little cost and effort, you can prevent most of the problems they cause using currently available methods. Research efforts can result in even more cost-effective, environmentally sound fire ant management systems.

Are fire ants still moving west and north?
Yes, and south, too. They have spread west to eastern New Mexico (Donna Anna County) and have crossed the Rio Grande River into northern Mexico. Their northward spread has reached the middle of Oklahoma where their survival depends on freezing soil temperature conditions. Cold winters tend to push them back. Western spread is largely dependent on availability of surface or ground water. However, with human assistance they have begun to infest parts of California where they are found mostly in urban areas, creek bottoms and irrigated land.

Why do fire ants appear to sting at the same time?
Fire ants are sensitive to vibration or movement and tend to sting when the object they are on moves. For example, when fire ants swarm up a person’s leg, the person jerks or moves. Usually, whatever causes one ant to bite and stings triggers the other ants to sting to the same response. Although fire ants emit communication chemicals, called pheromones, to elicit specific behaviors (alarm reaction, trail formation, queen recognition pheromones have been documented), there is no known pheromone stimulating ants to bite and sting.

Are fire ant stings lethal?
Only a very small portion of the population, around 1%, are hypersensitive to ant venom and will experience lethal allergic reactions. Very young and old people and those with suppressed immune systems are most likely to react severely to one or more stings. However, even healthy individuals may experience severe reactions such as anaphylactic shock if they suffer from a multiple stinging incident.

What should I do if I get stung by fire ants?
There isn’t much you can do, except watch the affected area for excessive swelling, itching or redness, or other symptoms like shortness of breath, thickening of the tongue, sweating, etc. that could indicate a severe systemic allergic reaction. If this occurs, seek medical attention. Otherwise treat stings as you would stings of other insects and keep them clean and intact to avoid secondary infections.

What if I have an allergic reaction to a fire ant sting?
Seek medical help immediately! If you are uncertain how your body will react, be sure to let someone know what has happened. It is best to be with other people that can assist you, if necessary.

Are fire ants as lethal as killer bees?
This is kind of like comparing apples to oranges. They both attack en masse and can both cause fatal allergic reactions, but that’s where the similarities end. Africanized bees can overwhelm and kill even healthy non-allergic people, but encounters are rather rare. Fire ants can’t overwhelm a healthy, mobile person and even hundreds of stings are rarely fatal. But, fire ant mounds are extremely common. The chance of being killed by bees is higher if you encounter them, but the chance of being killed by fire ants is greater only if you are highly allergic, or cannot quickly get away from them. The chance of either is small.

Fire ants are killing the quail, deer, lizards, songbirds, horn toads, etc. Why isn’t anything being done?
Things are being done, but it’s not an easy problem to solve. First, using today’s chemical methods of imported fire ant control provide only temporary suppression and, on a per area basis, costs money for each treatment. Wildlife inhabit very large areas, making the cost of periodic treatments prohibitive. Research is being supported to document the impact of the imported fire ant on wildlife and evaluate management approaches such as the establishment of natural enemies of fire ants from their native habitat. While some wildlife species are undoubtedly declining due to fire ants, there are other factors influencing the decline, such as land use practices and weather extremes. There is hope that the biological control agents released and established in any parts of the state and currently under investigation will permanently reduce imported fire ant populations.

Are fire ants killing my trees?
The ants are mainly using the trees as a nesting place. Ants in mounds occurring at the base of the trunk are probably not causing any damage to well established trees, and may actually be helpful by preying on other insects that are feeding on parts of the tree, and reducing compaction by tunneling in the soil. In Florida, however, imported fire ants do girdle trunks and kill newly planted citrus trees.

Why do fire ants get into laundry?
Laundry piles are convenient places that present lots of tunnels for the ants. They may be attracted to moisture or food residue or oils on soiled clothing. Often, reports of ants in laundry occur following a flood or severe drought. Ants are observed in utility rooms, bathrooms or near the water heater where they have access to the area from outside. When it floods they move into any good dark place, but in drought conditions they tend to move to moist areas.

Can fire ants be eradicated completely?
Red imported fire ants cannot be eradicated completely with methods available today in large areas of infestation like in the southeastern United States. But with proper control methods, they can be reduced or eliminated temporarily from small areas. Their biology and spread make it economically, technically and ecologically impossible to eradicate them from larger areas. However, recent efforts have been made to eradicate this ant species from small isolated infestations in California and around Brisbane, Australia. To date, these efforts have not been documented to be a success.

What is the best product for killing fire ants?
Texas Extension Service Extension does not endorse specific products. However, educational materials produced by Extension specialists provide information that will allow you to make the best choice for your situation. Texas A&M AgriLife Extension can convey research-based information on the performance of products that have been scientifically tested.

How do I eliminate fire ants from my yard?
There is no single, easy answer for every situation. Most people with more than a handful of mounds (5 ant mounds per ¼ acre yard or 20 per acre) will be satisfied with just a bait or the “Two Step Method”, which can provide 80 to 90% reduction of ant mounds in the treated area and works best on larger landscapes such as city blocks, neighborhoods or homeowner associations, school grounds and parks. Other methods may more suitable for smaller lots, where greater control is required or where fewer ants occur and native ant preservation is desired.  Remember, no method is 100% effective all the time, though some come close, and no method is permanent. The ants will re¬invade, with new colonies probably appearing after the next rain, and certainly within a year.

What is the “Two- Step Method” for controlling imported fire ants?
The Two Step is a proven method of reducing imported fire ant populations in heavily infested home lawns and ornamental turf. Briefly, it is the: 1) once or twice per year broadcast application of a bait product, and 2) treating unwanted active nuisance mounds at any time between these broadcast treatments using an individual mound treatment such as a dust, granule, bait, drench insecticide or home remedy such as use of very-hot water as a drench. By allowing for the bait treatment to take effect this method reduces the over-reliance on use of individual mound treatments and is suitable for treating larger areas. This approach is more cost-effective and environmentally friendly than most other chemical approaches, and “organic” options for the products selected are available.

Why tackle fire ants in the fall?
An ideal time to apply bait-formulated fire ant insecticides is from late August through October to allow the baits to reduce fire ant populations over the winter. Many bait products are somewhat slow-acting. Bu applying the in late summer or early fall, ant mound numbers will already be suppressed by early spring. Because bait product performance depends on foraging ants to retrieve the bait particles, applying them too early in the spring in cool weather (below 65°F) will be ineffective. Also, early spring application of slower acting products will not produce maximum effects until later in the spring or early summer. Fall applications are especially good for agricultural sites such as hay pastures where the first cutting is the most valuable.

It’s been dry and I don’t see any fire ants. Are they still around? Why should I treat them now?
The ants are still there, but the colonies are just not making mounds because of the hard, dry soil caused by heat and drought. They are nesting deeper in the ground during the day and the worker ants come out to forage during cooler parts of the day or at night. Ants are often more of an indoor problem at this time, as they come in seeking food and water. Treating with a bait product now can be very effective since the ants are weakened anyway. Baits can work quite well if the ants pick it up while foraging. In hot, dry periods, it is best to treat in the late afternoon or evening. Using individual mound treatments during hot, dry conditions is not a good idea because mounds are difficult to detect and/or the ants are nesting deeper in the ground.

Which bait should I use? How long does it take for baits to work?
The key to using baits is patience. Applied properly and using a fresh bait product, a broadcast application will give 80% to 90% control, rarely 100%. For instance, products containing the active ingredient, indoxacarb (Advion®), are the fastest-acting, providing maximum control within about 2 weeks, while baits containing hydramethylnon (Amdro® and others) give maximum control in 3 to 6 weeks. Products containing ingredients known as insect growth regulators (IGR’s) such as Extinguish® (methoprene), Distance® or Esteem® (pyriproxyfen) or Award® (fenoxycarb), when applied late in the year, may take several months to provide maximum control, but will suppress ant colonies for a months. One approach, for example, for heavy imported fire ant infestations is to treat with Amdro® first for fast knockdown, then come back with Award® for longer duration control as ants start to reinfest the area some months later. One product, Extinguish Plus is actually a blend of hydramethylnon and methoprene that provides rather quick suppression that lasts longer due to the IGR ingredient. See our Broadcast Bait section for more detailed information.

We tried using baits, but they don’t seem to work.
Baits work well if they are used properly. The thing to remember is the ants collect the bait as a source of food. Putting the bait out at the right time of day, and at the correct rate (usually 1 to 1 1/2 lb/acre but varies by product and formulation) is critical. If the ants are not actively foraging, they will not pick up the bait. The best times to apply bait applications occur between 65 and 95°F – generally mid-morning after the dew has evaporated, or late afternoon on hot days when the air begins to cool. Apply a small amount of bait or other food lure such as a potato chip in the area to be treated. If ants are all over it within 45 to 60 minutes, the bait is fresh and the ants are foraging! Always read and follow closely the directions provided on the product label before using any pesticide.

When and how often should I reapply the bait?
The fall application is important because it will help suppress ants by the following spring. Reapply when imported fire ant mounds begin to appear again. Generally, if you make a spring application, suppression should last until that fall, when the next application should be made. Re-infestation depends on size of area treated and frequencies of mating flights. Larger areas experience less colony immigration from untreated adjacent properties. During favorable colony development conditions and wet years, mating flights may be more frequent and intense, resulting in more newly formed colonies that appear one to two months following a successful mating flight.

I can’t afford to treat for fire ants.
If you have a 1/4 acre lot (100 x 100 feet, 70 X 150, etc.) you would need less than 1/2 pound of a bait product. A pound costs around $10 and yields two applications, with some to spare. Within a month or so, it would likely get ants down to a level you wouldn’t notice. For faster control, treat individual nuisance mounds after broadcasting a bait product. See our Broadcast Bait section for cost comparisons among products. It’s really not that expensive, if done right.

Which is best product to use?
There are over a hundred products labeled for use on fire ants and other ant species, but these products contain only a dozen or so common active ingredients. See our Broadcast Bait section for product names and information. In general, most products are effective and pose minimal risk when applied as directed. The trick is to compare characteristics of the active ingredients, concentrations and price (or the cost per ant mound treated). Buy the most appropriate product for your situation and use it strictly according label directions.

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What are some options for controlling fire ants inside the home?
The most important step is to identify the ant species and locating the nesting site. For ants nesting indoors, some products labeled for indoor use can be applied, including bait formulations, which foraging worker ants collect and take back to the colony to feed the queen. Trails of foraging ants can be sprayed with a contact insecticide, but these treatments do not directly affect the colony and may cause colonies to divide into a number of smaller colonies. Read and follow the directions on the product label for best results. Be sure to keep products away from small children and pets. Treating ants in the landscape outside will also help control some ant species, particularly imported fire ants that foraging inside from outdoor colonies or occasionally migrate indoors to nest. Finally, a band of contact insecticide can also be applied around the perimeter of your house to provide a barrier against invasion.

What is the safest product for my children, pets, chickens, etc.?
Always follow the directions provided on the product’s label. For insecticides registered by the Environmental Protection Agency (EPA), labeled products pose minimum risk to people and the environment when applied as directed.  You can use a less toxic material and apply it so that there will be little contact. The main concern is to not put a contact insecticide in high concentrations where children and animals can contact it, including storing insecticides where they are inaccessible.  Bait products, when broadcast applied, not only have very low toxicity, but are scattered very thinly and fall down in the grass where few things other than ants can encounter them. Granular and dust products will remain on the soil surface where potential contact can occur unless the material is watered in after application. Drenches may be a better individual mound treatment choice. Keep animals and kids away from treated areas as directed or until vegetation and the soil surface are dry.
What are some considerations when using insecticides around water and well heads?
Much of the same information holds true as for ant management around children and animals, but there is also the danger of ant mound drenches containing contact insecticides running off either immediately or after a rain. Selecting products with ingredients known to be less toxic to aquatic organisms can help. Some product labels, such as products containing fipronil, specify how far from the edge of a body of water a chemical can be applied. When broadcast-applying a bait product, make sure not to get bait particles in surface water as they may be eaten by fish. Contact the manufacturer for answers to questions about their products.
Is there anything I can use that isn’t a pesticide?
A pesticide is anything that kills pests. However, some options do not rely on chemicals formulated to kill insects. Using very hot water is somewhat effective for individual mounds. Approximately 3 gallons of very hot water poured onto mounds will eliminate ants about 60% of the time. Drench mounds on cool sunny mornings when the ants are close to the surface. However, you will risk damaging plants, grass, and even burning yourself. Some home remedies such as instant grits thought be eaten by ants and swell in their stomachs and cause death when placed on the mound, have demonstrated to be ineffective, in this case because worker ants cannot ingest particles larger than 2 microns.

Are there organic methods to control fire ants?
Fire ant control methods considered to be “organic” usually include cultural, physical, mechanical and biological control techniques, but some chemical treatments such as plant-derived (botanical, such as pyrethrins or d-limonene) and microbial-produced (such as spinosad)  insecticides are considered to be “of natural origin,” or organic. Some products are certified as organic by OMRI (Organic Materials Research Institute). Regardless of chemical origin or preparation, the Texas Fire Ant Project promotes the use of the least toxic methods. OMRI certified organic products such as bait and mound treatments using products containing spinosad or mound drenches using products containing pyrethrins or d-limonene can be used with the Two Step method.
Are there any biological controls for fire ants? I heard about a fly that is supposed to kill fire ants, what’s the story on that?
The University of Texas and the United States Department of Agriculture (USDA) have been conducting research on fire ant parasitic phorid fly species as one of several potential biological control agents for helping to control fire ants. Three species have been released and established in parts of Texas and are spreading naturally to adjacent areas. However, documentation about their impact on fire ant population levels has been published to date. Even in South America where the imported fire ants and parasitic fly species come from, the flies only affect about 3% of the worker ants in a colony. Some biological control agents that have already been marketed include predaceous mites, parasitic nematodes, and the fungus called Beauveria bassiana. Scientific studies continue to be being conducted to evaluate the effectiveness of some of these natural enemies, but others remain untested or have not been shown to be highly effective.
Why can’t I just pour gasoline on the mounds?
Don’t do it! It probably does not kill the entire colony much of the time, it is dangerous to handle, it kills any plant material it touches, and at least some of the residue remains in the soil and may leach or run off into ground and/or surface water.
Why don’t we use Mirex?
Mirex was an effective ant killer, but it was one of the most persistent compounds ever made. Mirex belongs to a group of chemicals that have mostly been banned from sale or use. Their ingredients, or their degradation products, accumulated in biological systems.
Can I purchase and spread fire ant bait on my yard without a “Private Applicators License”?
On your own property or on other private property as an unpaid volunteer, non-licensed private individuals can apply bait products. None of the baits are restricted products, but several may only be obtained from distributors to professional pest control operators or landscapers. See our Broadcast Bait section for over-the-counter baits at consumer retailers.
I assume a license would be required to spread fire ant bait and insecticides as a commercial business and on public rights-of-way.
If you are paid for your service in urban or agricultural and rural areas, you will need a license from the Texas Department of Agriculture (TDA), which provides commercial or non-commercial licenses.  On public school grounds, permission and supervision must be obtained from the designated IPM coordinator for that school. For rights-of-way, permission to treat must be obtained from the agency managing the property (e.g. Texas Dept. of Transportation).

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Does the worker who is spreading the bait have to be licensed or can he/she work under a licensed supervisor?
If fees are rendered for the service, workers must work under the supervision of a licensed pest control operator.
Is the State of Texas or Texas A&M AgriLife Extension offering pesticides for fire ants at a reduced cost for homeowners?
None of the funding provided by the Texas legislature to implement the Texas Imported Fire Ant Research & Management Project can be used to buy or apply insecticides. The objectives of the educational program being conducted by Texas A&M AgriLife Extension include encouraging homeowners and/or community groups to 1) decide what methods of control are right for their situation, and 2) use these methods for sustainable or long-¬term suppression by doing it yourself or with your neighbors, or with the help of a professional pest control service.
I think all pesticides are dangerous and harm the environment. Why should I be paying tax money to encourage people use them?
Pesticides vary greatly in toxicity to the target organism, the user, and the environment. An even greater danger occurs when people misuse or overuse pesticides. One of the goals of the Fire Ant Project is to educate people on the selection and proper use of the least toxic methods to control imported fire ants. In this way, we hope to decrease overall pesticide use and make it safer for people and the environment at the same time. There is also a lot of effort and funding support for ongoing research to develop nonchemical methods for fire ant suppression.

All that tax money for fire ant research is a waste. How come I don’t ever see any results?
Research is a slow, methodical process. Even if an exciting discovery is made in the laboratory, it must be tested in the field. Then its practical use must be proven. The process may be slow, but the investment in research is the only option that can potentially provide major advancements in improving today’s methods of imported fire ant control.

Why don’t we have a program like the one that solved the screwworm problem?
Red imported fire ant biology is different from screwworm biology. With funding from the Texas Fire Ant Project, researchers are beginning to investigate potential behavioral, genetic and reproductive factors that could be exploited as possible components in controlling fire ants. Even if the same sterile male technique as used in the screwworm problem were possible to use with red imported fire ants, the technology to raise, sterilize and make timely releases of high numbers of sterile male ants has not been developed.
Why should I care about fire ants if I live in an area that doesn’t have them?
You should care about fire ants because you could have them soon! The Texas Fire Ant Project is funding extensive surveys to detect and document the occurrence and spread of the red imported fire ant (and native ant species that compete with it for food and resources). Where detected, appropriate actions can be taken to slow or even stop their spread.

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