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The Story of the Little Fire Ant: Modern Medicine Learns From Indigenous Cultures

Wasmannia auropunctata

The little fire ant, Wasmannia auropunctata, is an invasive species and also a common cause of a previously mysterious eye affliction known as West Indian punctate keratopathy or Rice’s keratopathy. (Photo credit: Lyle Buss, University of Florida)

By John P. Roche, Ph.D.

Lesions of the cornea that cause white discolorations of the eye, called leukomas or corneal opacities, have been discovered for decades in humans, domestic animals, and wild animals. Sometimes called West Indian punctate keratopathy, Florida spots, or Rice’s keratopathy, this condition was a mystery to the medical community. But a new paper in the Journal of Medical Entomology reports that the cause of these lesions has been known for a long time by indigenous peoples in Colombia. What is the cause? Wasmannia auropunctata, also known as the little fire ant.

Diego Rosselli, Ph.D., of the Pontificia Universidad Javeriana in Colombia and James Wetterer, Ph.D., of Florida Atlantic University co-authored the report, in which they gather knowledge on the condition from disparate sources to better inform the medical community.

The corneal lesions were first reported in the medical literature in 1968 by Noel Rice, who noticed it in immigrants from the West Indies in London. Rice came to the conclusion that the condition was caused by trauma to the eye. The lesions were then reported in cats in Florida in 1979 and in dogs in Brazil in 1997. In 2004, corneal lesions were reported in cats and dogs in Martinique, but they were only found in animals that lived outdoors.

Other potential explanations for the corneal lesions were proposed in the literature, including viral infections, bacterial infections, and inflammation resulting from exposure to the microfilariae of the parasitic worm Onchocerca volvulus, the worm that causes river blindness.

None of these researchers were aware of the true cause of the lesions—but indigenous cultures in Colombia have known the cause for a long time—stings from the little fire ant, Wasmannia auropunctata. The lesions could arise from other causes, but, as Rosselli and Wetterer write in their paper, if there was no trauma to the eye and there was no infection, W. auropunctata is the cause.

The little fire ant originated in the lowlands of Central and South America. Carried by human trade, it has spread to Florida, Africa, Israel, Australia, and many Pacific islands, including Papua New Guinea, Hawaii, the Solomon Islands, and the Galapagos. The ant creates a toxin that, when it stings the eye, can cause corneal lesions. The stings often occur when humans or animals blink in response to the presence of the ant, and the blinking triggers the stinging.

“Indigenous knowledge, which is normally neglected, has observed the association for many years. Thus, scientists should try to be aware of discoveries in fields different from their own,” says Rosselli.

Asked what the biggest surprise of the study was, Rosselli says, “Ants represent a large proportion of all insects (and therefore of all animals), but their association to human diseases has been scarcely explored.”

Regarding next steps in this research, Rosselli says research on the chemistry of little fire ant toxins could be valuable: “I was surprised to know that despite the impact of this ant in agriculture, in animal diseases, and, with our paper, in human disease, very little is known about the toxins produced by the little fire ant (as compared with its larger relative the big red fire ant).”

As for possibilities for control of the little fire ant, Rosselli says results of studies have been mixed. In Florida, for example, insecticides were very effective in reducing populations of the little fire ant. But, when the insecticide use is scaled back, the ants tend to return. Physical methods such as applying scalding water to colonies, or excavating and removing colonies, can also be effective. Biological control methods may offer the greatest promise. The little fire ant is more destructive in regions where it has invaded than in its native habitats, which might be a result of biological control from species present in its native habitats. Introduction of such biological control species might be effective in helping to control outbreaks in other regions. To prevent eliminating biological control species, insecticide baits are most effective if they focus on mounds with a colony of the little fire ant, rather than being broadcast to a wider area where other species could be affected.

Agricultural workers are sometimes exposed to the ants when harvesting products, in settings such as citrus orchards, cacao orchards, and palm tree plantations. Domestic animals are sometimes exposed when the ants are in their food bowls. Rosselli mentioned that goggles might be used by workers in some agricultural settings, such as palm tree plantations, and insecticides might be applied to animal food bowls to keep the ants away from domestic animals.

One characteristic that makes control of the little fire ant so problematic is that the ant is a “tramp species,” spreading throughout the world via human commerce. Increased inspections of agricultural products, and quarantines of products infested with W. auropunctata, could be useful components of control.

John P. Roche, Ph.D., is an author, biologist, and science writer dedicated to making rigorous science clear and accessible. He has a Ph.D. in biology, has published more than 180 articles, and has written and taught extensively about science. For more information, visit


  1. “But a new paper in the Journal of Medical Entomology reports that the cause of these lesions has been known for a long time by indigenous peoples in Columbia.”
    Change to Colombia.

  2. Little fire ants don’t build mounds, so the advice to “focus on the mounds” when treating is not valid. LFA baits must be widely broadcast, and when used correctly, should have little to no impacts on non-target species. LFA form super-colonies made up of many queens, working cooperatively short distances from one another, so there is almost a web or matrix (so bait needs to available over a wide area). It is important for people to understand that in order to treat correctly.

    • Yes, thank you Frances! I was disappointed to see the “mound” misinformation, and appreciate your corrections.

      Living in an area of Hawai’i where the little fire ants I’ve written an argument for and a message in a bottle to someone to take on leadership of a campaign to get the government to fund a biocontrol research program to bring LFA populations into balance. Without that, life will be hell after the ships stop bringing us the poison which is currently the whole thing keeping their numbers in check.

      Paradise or hell?—Hawaiian future depends on little fire ant biocontrol

  3. Hey, regardless of the errors, thank you for bringing light to a very unusual but serious epidemic. I had no idea that LFA had made it to Israel, that sounds like terrorism to me. I have lived in Hilo Hawaii on and off for years. Even from SoCal I am itching as a type this. These ants literally ruined my life, destroyed my boss’s business and killed several puppies. People I know, entire families have lost their homes.

    I am shocked at times, when I casually talk about LFA electrical damage causing fires and people have no clue what I am saying. “But ants are small?” Ya I know, trust me these are smaller, and they take wire insulation to kill the electricity. Subsonic/supersonic noise caused by wiring and bad grounds in circuits attracts them for some bizarre reason.

    A “colony” of LFA is a misnomer. Somehow these atypical ants do not have Queens, like typical ants. They are nomadic, travel with eggs, hunt in sexually mixed groups and infest tall trees. These ants have evolved with little sexual dimorphism (variation between sexes). The effect is a large mixed swarm of rapidly replicating micro scale predatory ground wasps. I have observed on several instances, groups of several thousand cross a paved road with about half the pack carrying at least two eggs or injured comrades.

    They climb trees and blow in the wind to cover a larger area faster. These ants are an economic devastation to Puna District and South Hilo as well as parts of Maui and even Kuai. I have tried to seek outside intervention, however the State of Hawaii is the highest authority which seems to regard the issue seriously. Nonetheless, Efforts are underway, progress has been made, people have been helped. I would like to put a shout out to Eucalyptus Globus Essential Oil as the only truly effective organic treatment with 100% success. I have experimented with different mixtures of all varieties and my own blends are premium.

    As much as damage to farmers is an issue for concern, the real threat is far deeper. The death toll to Hawaiian indigenous ground nesting birds, and even the Majestic I’o Hawaiian Kite Hawk is catastrophic. Entire areas of forest are reduced to dust the ants consumption. What cats and rats did not erase these ants are rapidly making short work of. Interaction with a group LFA infestation of a fern tree (Hapu Upulu) has been demonstrated to kill adult male Polynesian Boars in only a short time. The full scope of the ecological damage, just on the Big Island alone, is without measure.

    Thank you for bringing this topic to light, it warms my heart to know the community is becoming more aware of nature of the issue. Who knew something I could not see without my glasses could ruin everything.

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