Key takeaways
- The red imported fire ant arrived from South America between 1933 and 1945 and is now the main fire ant in South Florida lawns.
- A mature colony typically holds about 80,000 workers and can reach 240,000, with a queen laying up to 1,500 eggs a day (UF/IFAS).
- About 95% of the venom is alkaloids, which cause the burning pain and the white pustule that forms about a day later.
- Only about 20% of a colony forages at any one time, so spraying the ants you see does little to the colony.
- Florida's sandy soils produce low mounds that are easy to step on before you notice them.
In this article
Fire ants are small, reddish-brown stinging ants that live in huge underground colonies, build mounds in sunny lawns and attack in numbers when their nest is disturbed. In South Florida, the species behind almost every painful encounter is the red imported fire ant, Solenopsis invicta, an invader from South America that thrives in irrigated yards and warm weather.
Fire ants are worth understanding, not just avoiding. Their colony structure, feeding habits and way of reproducing explain why stepping on a mound hurts so much, why new mounds appear after rain, and why spraying the ants you see rarely solves anything. This guide covers the biology, from the queen to the sting, with a South Florida focus.
Meet the Red Imported Fire Ant
The red imported fire ant is native to central South America. According to UF/IFAS, it reached the United States from Brazil, arriving at Mobile, Alabama, or Pensacola, Florida, sometime between 1933 and 1945. It has since spread across most of the southeastern United States, including Florida.
Florida also has native fire ants, and there is a black imported fire ant and a hybrid elsewhere in the South. Telling fire ant species apart reliably takes a specialist, which is why identification comes before any treatment plan. Our fire ant species page covers the identification details.
How to Recognize Fire Ants
- Size: workers range from 2.4 to 6 mm, about 1/8 to 1/4 inch.
- Mixed sizes: large and small workers come from the same mound. Scientists call this polymorphism.
- Color: reddish-brown to black, often with a darker abdomen.
- Behavior: when a mound is disturbed, workers pour out and run up grass blades, shoes and legs to bite and sting.
- Mound: a dome of loose, worked soil in a sunny spot.
Inside a Fire Ant Colony
A fire ant colony is a highly organized family. Fire ants do not have a separate “soldier” caste. Instead, workers come in many sizes, and their size shapes their job and lifespan.
| Member | Role | Lifespan (UF/IFAS) |
|---|---|---|
| Queen | Lays all the eggs; up to 1,500 a day in a mature colony | About 2 to 6 years |
| Minor workers | Smallest workers; care for brood and forage | About 30 to 60 days |
| Median workers | Mid-sized foragers and defenders | About 60 to 90 days |
| Major workers | Largest workers; defend and handle large food | About 90 to 180 days |
| Winged males and females | Leave the colony to mate and found new colonies | Males die after mating |
| Brood | Eggs, larvae and pupae, the white objects you see in a broken mound | Egg to adult in 22 to 38 days |
Source: UF/IFAS EDIS, Red Imported Fire Ant (IN352)
Development is fast. Eggs hatch in about 8 to 10 days, the larval stage lasts 6 to 12 days and the pupal stage 9 to 16 days. A new colony can have several thousand workers within about six months. A typical mature colony holds about 80,000 workers, and large ones reach about 240,000.
Some colonies have one queen and others have many. Multiple-queen colonies produce more mounds, packed closer together. UF/IFAS extension guidance notes that single-queen colonies produce about 40 to 150 mounds per acre, while multiple-queen areas may have 200 or more.
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What Fire Ants Eat
Fire ants are omnivores. Workers eat dead insects, earthworms and other animals, prey on live insects, and collect honeydew from plant-feeding insects. They also seek out sweets, proteins and fats, including food in homes and pet bowls. UF/IFAS Gardening Solutions points out that fire ants feed on grease and oil more than other ants, which is why fire ant baits are often oil-based.
Larvae cannot eat solid food at first, so workers bring liquids back to the nest and share them. That food-sharing habit is the key to baits: workers carry the bait home and feed it to the brood and the queen.
Only a portion of the colony is out feeding at any time. UF/IFAS Gardening Solutions estimates that only about 20% of the colony is foraging at a given moment, so killing the workers on the surface leaves most of the colony untouched.
Where Fire Ants Live in South Florida
Fire ants prefer sunny, open ground, and well-kept landscapes suit them. Typical spots include:
- Lawns, especially along driveways, sidewalks and garden edges
- Parks, playing fields, school grounds and canal banks
- Around trees and stumps and under pavement and slabs
- Around AC pads, pool equipment and electrical boxes
Depending on the soil, mounds can reach 18 to 24 inches high, and the tallest ones are found in clay soils. Florida is different. UF/IFAS notes that, because of Florida’s sandy soils, fire ants may not build sizable mounds, so many South Florida mounds are low and easy to step on.
Rain shapes what you see. After heavy rain, colonies may move to higher ground or even indoors to escape saturated soil, and floodwaters can turn a whole colony into a floating raft. Our article on how fire ants survive flood waters explains that remarkable behavior.
How Fire Ants Reproduce and Spread
New colonies start with mating flights. UF/IFAS reports that a colony releases winged males and females six to eight times a year, from spring to fall, with up to 4,500 winged ants per flight. Flights usually happen around midday on a warm (above about 74°F), sunny day following rain.
After mating in the air, males die and new queens land, shed their wings and dig in to start a colony. In the southern United States, up to 97,000 queens may be produced per acre per year. Winged fire ants often end up in swimming pools, a familiar sight in South Florida backyards after a summer shower.
Colonies also move. Disturbing a mound repeatedly often makes the colony relocate rather than die, and untreated land nearby keeps supplying new queens and colonies.
Why the Fire Ant Sting Hurts So Much
A fire ant grips the skin with its jaws, then stings, often several times. About 95% of the venom is made of alkaloids, which cause the burning pain and the white pustule that forms about a day after the sting, according to UF/IFAS. The rest of the venom contains proteins that can trigger allergic reactions in sensitive people.
The CDC describes a burning sensation followed by red bumps that may develop into white, fluid-filled pustules within a day or two. UF/IFAS Gardening Solutions adds that the effects can last up to 10 days and can become infected if the pustules are broken open.
Why Fire Ants Matter Beyond the Sting
Fire ants are more than a painful nuisance:
- Property: UF/IFAS notes that nest cavities under patio slabs can make the concrete fall and damage sidewalks, and extension guidance reports that fire ants chew electrical insulation and cause short circuits in AC units and other equipment.
- Wildlife: fire ants can reduce populations of ground-nesting birds and rodents.
- Agriculture and gardens: they feed on young growth of many crops, a topic covered in our guide to fire ants in your garden.
- Outdoor life: mounds in lawns, parks and playgrounds keep families off the grass.
Fire ants are only one of several invasive ants in South Florida. To compare them with bigheaded ants, little fire ants and others, see Florida’s most aggressive ant species.
What Fire Ant Biology Means for Control
Every effective control method follows from the biology:
- Target the queen. Baits work because foragers share them with the brood and the queen. Treating only the mound surface or spraying foragers misses most of the colony.
- Treat when ants forage. UF/IFAS extension guidance recommends applying bait when the ground and grass are dry, no rain is expected and soil temperatures are about 65 to 90°F, and in midsummer in late afternoon or early evening.
- Skip the myths. Club soda, grits, soap, wood ashes and shoveling mounds together do not work, according to UF/IFAS. Gasoline is flammable, harms grass and soil and often just makes the colony move.
- Expect reinfestation. UF/IFAS states there are no control methods that permanently eliminate fire ants from an area, so ongoing monitoring matters.
If mounds keep returning, Toro’s lawn spray service starts with a free inspection to identify the insects in your lawn, followed by a control program with power lawn sprays and granules and follow-up visits. Toro has protected South Florida yards since 1969, and if the bugs come back, so will Toro, at no additional cost to you.
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305-594-4767Frequently Asked Questions
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Sources
- Red Imported Fire Ant, Solenopsis invicta Buren, UF/IFAS Extension
- Managing Imported Fire Ants in Urban Areas, UF/IFAS Extension
- Fire Ants, UF/IFAS Gardening Solutions
- Insects and Scorpions at Work, Centers for Disease Control and Prevention (NIOSH)
Educational content. This article is for general information about pests in South Florida and is not medical, legal or professional advice. If you have a bite, sting or allergic reaction, contact your doctor; in an emergency, call 911. Pest problems vary from home to home, so a licensed professional should inspect before treatment. When using any pesticide, always read and follow the product label.
