The Walking Red

Red Imported Fire Ants

North Carolina Increases Quarantine Area for Red Fire Ants
January 18, 2016


If one were to make a big-budget Hollywood movie about an invasive species, it would probably resemble a zombie picture. A completely foreign life form enters an unsuspecting ecosystem. The local organisms don’t know what the invader is, until it’s too late. The invaders feast and multiply and feast and multiply until they dominate the ecosystem and have to move on to the next one.

These invasions are happening all over the place. Pythons are reaching huge numbers in South Florida, millions of lionfish patrol the reefs of the southern US Atlantic coast and the Gulf of Mexico while kudzu vines have grown over three million hectares of the Southeastern United States.

Very much like a zombie movie, the devastation these species cause paints a grim picture, but every good zombie movie has that one horrifying shot of thousands of advancing zombies, single-minded in their appetite for brains. (Un)fortunately, we don’t see hordes of pythons slithering out of the swamps at the same time, the groups of lionfish are too busy poking around the gaps in reefs where little fish swim to get a good shot, and a shot of kudzu growing does not make the most gripping cinema.

(Un)luckily for us, we have the perfect species in North Carolina for our horde shot: the red imported fire ant, for which the North Carolina Department of Agriculture and Consumer Services just announced a quarantine of Halifax, Macon and Graham Counties.

To some, these tiny, red, biting ants native to South America may not even seem like some exotic invasive species, as they are not exactly new to the area.

Their first U.S. sighting was in Alabama in the 1930s. The first time they were seen in North Carolina was in Brunswick County in 1957. Over the past 50 years they have slowly spread to the point where 71 of North Carolina’s 100 Map of Quarantined Areacounties are infested with them.

The new addition to North Carolina’s quarantine will bring that total to 74 counties. The national quarantine stretches as far north as Virginia and continually west to Texas, with spots in New Mexico and California: 320 million acres.

Red imported fire ants are the perfect cast for a zombie horde, and what makes them fit the bill so well is why both the state and Federal Government is trying to stop them.

First, they have huge numbers and can spread quickly. A typical colony will number roughly 80,000 up to 150,000 workers, and each acre of infested land can produce up to 97,000 queens per year. Although most of those queens will die, each has the capability of building another colony. Red imported fire ants also mate in flight, so they can fly a reasonable distance to establish a new colony.

The colonies themselves are housed in large mounds that in some places can number up to 300 per acre. The mounds make preparing land for agriculture difficult.

Their numbers and rapid spreading ability help them fit the second aspect of their zombie role—their ability to conquer and consume anything in their path. Every one of those 80,000 workers in the colony has only one job: bring back food.

Food can mean sugars and fats from inside a home. On farms it can mean seeds, leaves, roots and nectar, which can harm crops. Above all, though, red imported fire ants are carnivores. They can eat anything that nests in the ground: birds, bees, other ants, worms and even small mammals. A large enough number of fire ants can drive out almost anything that lives in the ground.

Red Fire Ant FrontThird, as anyone who has ever been stung by one knows, red imported fire ants have the dangerous bite of a good zombie, and they are not stingy with it. The red fire ant actually bites and stings. It will bite down to hold itself in place before using the stinger in its tail, and that stinger carries a venom that will create stinging white pustules, as well as some carbohydrates that can cause an allergic reaction in some people.

What’s more, when their mound has been damaged, they will swarm out to attack whatever did the damage. When the first ones bite and sting, they release a pheromone signal to the following ants to bite and sting as well.

Fourth and finally, just like zombies, they are very difficult to stop. The classic zombie movie trope is that the only way to stop a zombie is to get it in the head. Red imported fire ants are similar, except the head is the queen. The trouble is, the queen isn’t as easy to reach as you might think.

Red imported fire ants are largely resistant to flooding. They will cluster up around the queen and then float along until the cluster hits a tree, at which point the queen and many workers will climb to safety.

Insecticides are effective, but again the trouble is getting it deep enough into the colony to get the queen to feed on it. Insecticide can be “watered” into the mound but there is no guarantee of the drenching reaching the queen.

It is possible to inject the poison in with a high-pressure hose, which is a more effective solution, but there is a danger of the insecticide leaking and there is still no guarantee of killing the queen.

The most effective method is by baiting the ants with insecticide-laced food that the foragers will bring in to kill the queen. There are some problems there too, though. The toxic chemicals sometimes degrade in sunlight and could therefore be useless by the time the ants find them. Also, if the colony is fed well enough, they may not take the bait.

Like every good zombie movie, there is also a “last act of a desperate government” method as well. There comes a point in every movie where the military decides to napalm or atom bomb an entire city as a last attempt to contain theRed Fire Ant virus. The fire ant equivalent is “broadcast baiting.” Just like the baiting example above, it involves putting out poisoned bait for the ants to find, but broadcast baiting involves spreading it over a field with many colonies.

Just like normal baiting, broadcast baiting is effective when the poison makes it down to the queen, but on top of the issues with normal baiting, broadcast baiting comes with the potential of poisoning other organisms if they find the bait first.

The last methods of fire ant eradication involve introducing another invasive species to attack them first. Protozoans, fungi, parasitic flies and even other species of ants are all being explored as possibilities to fight the fire ants on their level.

The quarantine itself is focused on stopping the fire ants’ original source of transportation, the one that brought them to the U.S. in the first place: people.

As dirt-dwellers, fire ants will go wherever their dirt goes, and scientists believe the first U.S. fire ants came from Brazil into the port of Mobile, Alabama in the trading ships’ ballast, weights used to keep ships from capsizing. Older ships would often use rocks and dirt for ballast and scientists think this ballast dirt brought the first fire ants to the United States.

The quarantine regulates the movement of plants, soil, sod and any equipment used to work with those things into and out of the quarantined counties. Special permits are required to move these objects.

This is where the movie ends for now: the zombies are still multiplying and taking over more space, but the government is taking actions to stop them. The take-home for the viewers? Red imported fire ants spread quickly enough on their own. Don’t help them out. Be very careful when moving plants or equipment around, check for the ants when you do, and whatever you do, try not to step on an ant mound. You won’t turn into a zombie, but you will never forget how it feels.

— Daniel Lane

Daniel Lane covers science, medicine, engineering and the environment in North Carolina.


GSK