Invasive pests. With an absence of natural predators – they can wreak serious havoc in our garden and, sometimes our environment. There’s a category of invasive creatures which isn’t lethal to our plantlife, but it still strikes fear in the heart of many gardeners. I’m talking about fire ants, and the sting of these creatures is more than just a painful nuisance. It’s also the cause of the loss of human life every year in the U.S. So, it should come as no surprise, fire ant control is a high priority for many.
Fire ants used to be a concern only for those of us living in the southeastern states, but their spread has now breached California, into Oklahoma and as far north as Virginia. They aren’t just an American problem either. Australia, South Korea, Japan, and many other countries have been the unhappy recipients of red fire ant invasions, thanks to some of these resilient insects hitchhiking on board ocean shipping cargo.
Dr. Robert Puckett is with the Texas A&M Department of Entomology. He and his colleagues there study fire ants and other insect pests to determine how to combat them. You might not know it, but fire ants have been studied intensively for decades. After all, our country spends about $5 billion each year trying to manage this particular pest species, with minimal success so far.
Understanding the Enemy
There are over 12,000 ant species on our planet, and a few hundred of those belong to the fire ant family. It’s the red imported fire ant species, Solenopsis invicta, which are causing so much harm in North America.
In their native South American habitat, Solenopsis invicta are kept in check by many natural predators, including some species of pathogen and parasite. Plus, many South American ant species are more aggressive than their North American cousins at competing with fire ants for resources
You’ll know your property has been invaded by fire ants when you spot the mounds they form in the garden and landscape. The structure of the mound fans out laterally under the soil surface. It takes on an upside-down conical shape as it goes deeper into the surface. It’s not uncommon for a single colony to build two or three mounds.
Fire ants are extremely adaptable and will even work together to overcome a flood. As water levels rise in a fire ant mound, all the ants move toward the surface. Once water overtakes the whole area, the ants actually lock legs to float together like a living raft. The colony can remain buoyant for long periods until they come in contact with a vertical surface – like a tree or a wall. Then, they scramble up the surface until the area dries out, and they are able to build a new subterranean colony.
One thing fire ants have not yet adapted to is cold, rainy weather. A colony can survive extremely cold temperatures by retreating deeper into the soil. However, if a heavy rain pushes the ants up from the depths, it leaves them exposed to a lethal overnight freeze. That’s why regions of North America which are known for rain followed by severe cold have managed to remain safe from fire ant infiltration.
Some red fire ants form single-queen colonies, but most North American colonies follow a multiple-queen social form. Unfortunately for us, it’s the multi-queen colonies which are the most challenging to eradicate. These can be home to a dozen or more queens, and every queen must be eliminated in order to effectively destroy a colony.
Here’s the really bad news: Fire ant queens can fly – for long distances. So even when you do successfully eradicate a colony in your landscape, a new one will definitely be in your future.
Robert explains that, as often as once a month, fire ants take “nuptial flights” – usually after periods of dry weather. Queens and male workers develop wings just once in their life. Once that happens, they take flight in swarms and mate in mid-air. They can really gain altitude, so we often never see them. After flight, the males die. The queens which have successfully mated will drop to the ground, shed their wings and form a new colony.
So if you spot winged ants scurrying around a mound, those are the bugs which are suited up and ready to swarm and reproduce. In other words, those are your top priority targets.
A Sting to Remember
There’s a commonly-held belief that all things have a purpose. I agree with that philosophy in most cases, but invasive species are an exception. They may play a necessary role in their native habitat, but species labeled as “invasive” are so-named because they are so aggressive and lacking in natural predators, that they outcompete and destroy native species.
Native ant species can be a nuisance, but they are an important player in the soil food web and the ecosystem at large. The red fire ants which have invaded North America are aggressive and territorial. They stake first claim on all food sources and other resources that beneficial native ants need for survival.
Unless they are near the mound, identifying which is a fire ant and which is a native species requires some expertise. On the other hand, if you get stung, odds are good you are dealing with a fire ant.
Native species are typically very docile, unless they feel threatened. Robert likes to say that fire ants have a bad attitude. They won’t wait for a life-threatening situation to sting, they will aggressively attack anyone to cross their path.
Termites are commonly confused for fire ants, but you can distinguish these pests from each other when you know what to look for. Between the thorax and abdomen of a fire ant is a constriction – like a tight waistline. You might say that fire ants have an hourglass figure. Termite bodies have no constriction.
Another difference you can spot from a safe distance is antenna shape. Fire ant antennae have a sort of elbow – a long segment which transitions in a bend to several small segments out to the tip.
Of course, termites don’t sting either. They’ll just turn your home into a pile of sawdust.
What about that sting? Fire ants earned their name thanks to the fiery pain of their sting. Unlike some bee species, fire ants don’t lose their stinger or their life when they strike. They can (and probably will) sting over and over, but only the females. Males of the invasive fire ant species don’t sting. Thanks, ladies.
The female fire ants inject an alkaloid venom, but it’s our own allergic reaction which results in the tiny welts that itch like crazy and form white pustules. Unfortunately for some people, the reaction becomes more intense with age, and it can even become systemic – causing anaphylaxis. Each year, anaphylactic reaction to a fire ant bite is the cause of at least a few deaths in the U.S.
Fire ants are particularly hazardous in areas of the U.S. which are hit hard by flooding from rain or tropical storms. As residents wade or swim to shelter through fire ant-infested neighborhoods, they are at risk of coming into contact with living rafts of some very peeved fire ants just looking for something to climb onto. That is the stuff nightmares are made of.
Fire Ant Control
Researchers tried introducing a South American predator in hopes of curbing North American fire ant populations naturally. Phorid flies belong to the Pseudacteon insect genus and are one of many parasitic fly species. These flies were imported and released as a biocontrol in the southeastern U.S., and they have been successful in this country. So if fire ants have invaded your region, phorid flies are likely to be your neighbors too.
How do the flies find the ants? Well when a fire ant mound is disturbed, the insects emit pheromones to communicate to the rest of the colony that it is under attack. The alerted ants come rushing to the surface to defend the mound. As the defensive pheromones drift through the air, phorid flies are able to detect the plume from miles away and follow it back to the mound.
You probably won’t realize when phorid flies have arrived, because they are only as big as a fire ant’s head. They may be small, but they are bad news for fire ants. The female phorid fly injects an egg into a fire ant worker. The egg quickly hatches into a maggot, which feeds on the innards of the ant. The ant survives during the first 4-5 days of being parasitized – until the maggot works its way through the constriction at the tip of the thorax and into the head of the ant.
Once the maggot has fed inside the ant head, it matures into a fly and releases an enzyme which causes the head to separate from the ant’s body. That is how the mature fly escapes into the environment to parasitize more of the colony.
Unfortunately, phorid flies haven’t proven to be effective against fire ants in urban, inner-city areas. Researchers aren’t sure why that is.
One study examined how increased amounts of impervious surfaces (like concrete or asphalt) affected fire ant and phorid fly populations in cities like Austin and Waco, Texas. Fire ants were just as likely to colonize those areas, but phorid fly populations dropped. It’s possible that the flies require something for survival in natural habitats that urban areas don’t provide.
Unfortunately for gardeners, fire ants prefer to colonize in soil which has been disturbed – like our edible garden beds and newly-planted landscape areas. There are all kinds of anecdotal “treatments” out there being promoted as effective for eradicating mounds. So, what really works?
Some of the many effective products on the market contain a synthetic active ingredient. There are also many organic, naturally-derived options.
When it comes to any garden pest issue, I recommend following an IPM approach, and Robert suggests it as the best philosophy for managing fire ants as well. Integrated Pest Management (IPM) follows a principle that the gardener needs to determine what his or her threshold of tolerance is for the pest, and as treatment becomes necessary, the least toxic options are used first.
In other words – if you opt to treat, start with the mildest option. After treatment, observe the results. If the threat of the pest is still beyond your threshold for tolerance, it’s time to escalate to an option that is slightly less mild. Only as the mild options fail to solve the threat do you escalate up the ladder to more aggressive options.
When it comes to fire ants, Robert lines out the IPM approach this way:
Rely on biocontrols. You may have phorid flies in your area. Try alerting them to the presence of fire ants by disturbing the mound. Allow some time for the ant pheromones to attract the flies and for the parasitizing to begin to have an impact on the colony. If you can’t wait or don’t see evidence of parasitization, escalate to the next level.
Physically remove the colony. Robert’s team moves colonies often. After all, they need to get them into the lab for research. Fortunately, they have a little trick up their sleeves to avoid being stung in the process.
Team members coat the inside of 5-gallon buckets and the metal portion of sharpshooter shovels with baby powder. Only the talc-based powder works for this, so never use cornstarch-based baby powder to contain a colony. The talcum powder prevents the ants from scaling the sides of the bucket (or the handle of the shovel).
The mound – and the colony – are scooped into the bucket with the shovel. As they attempt to climb, they will wear the talcum powder off and will not be in a good mood, so it’s important to work quickly. Robert recommends banging the shovel onto the ground occasionally as you scoop to knock off any climbing worker ants.
It’s critical to dig deep enough to be sure to scoop out the queen or queens too. If a queen remains, the colony will become re-established.
Once they are in the bucket, what’s next? A good option would be to keep boiling water at the ready, so you can pour it into the bucket and kill the colony immediately. You could opt to relocate the colony, but that probably won’t earn you any friends.
Robert’s team brings the captured colony into the lab and places each bucket under a slowly dripping faucet. As the water rises, the fire ants begin to float, and team members scoop them (very carefully, of course) with a spatula into a container designed to hold the colony for study without soil.
If moving a mound isn’t your cup of tea, the next least-toxic option is boiling water. You may have heard or read that boiling water can kill a colony. It’s true. This is an effective option, however it may take more than one application. The only way to eliminate a colony is to kill all the queens, so every queen must be cooked.
As you pour boiling water onto the mound, the ants will inevitably move away from it. They didn’t make it this far by being stupid, right? So, the most effective application method is to start by pouring the water around the perimeter of the mound and spiral your way in toward the center. That will push more ants into the middle of the mound and potentially nearer to the surface to be killed by the boiling water.
Boiling water will just as effectively kill plant roots, so if the mound is next to plants, you’ll need to be especially careful.
Robert reports that a treatment of boiling water is successful about 60% of the time. Multiple applications can improve your likelihood of killing every queen and, as a result, the colony itself.
If boiling water doesn’t effectively eliminate the mound, Robert recommends insecticidal bait as the next best option. Baits exploit fire ants’ ability to forage for food.
These creatures will aggressively seek out and defend any food resource against native ants or other competition. So, there is little risk that non-target insects will be impacted by the bait – as long as you carefully follow the application instructions.
Fire ant bait products are usually made of corn grit granules. The grit is de-fatted – meaning the natural fats are removed from the granules. This prepares the material to receive the active insecticidal ingredient. The active ingredient, mixed with soybean oil, is absorbed by the grit.
Fire ant adults can’t eat solid foods. No wonder they’re so crabby. So, how does the bait work? Sometimes, the ant is able to remove and feed on the oil (along with the insecticide) from the grit. Usually though, the ant carries the granule back to the colony, and provides it to the brood of fire ant larvae developing within the mound. The larvae break the grit down into a liquified form that the worker ants can slurp up. Delicious.
The adult ants utilize the nutrients, but they also regurgitate the liquid to feed other members of the colony. Eventually, the liquid – and the pesticide – makes its way to the queen. That’s a complicated process, so it’s no wonder that it takes three weeks or longer from the time a bait is applied until the colony dies off.
Bait products use different active ingredients. The most common is spinosad – a natural product produced by a species of bacteria. It is a broad-spectrum insecticide, so it will kill other insects. Amdro is a widely-used synthetic bait product which also has the broad-spectrum ability to kill a wide range of species beyond the fire ant.
Since beneficial insects, like pollinators, are just as likely to die from these products; proper application is key. Over-application is a common mistake. More is better, right? Wrong. Putting more out won’t kill the mound any faster. Fire ants are such efficient foragers, they will seek out even trace amounts of food, and they will fight off any other creature that comes within range.
In fact, the recommended application rate for Amdro amounts to just eleven granules per square meter of space. That minuscule application will be tracked down by fire ants but the risk of other insects coming into contact is low. In testing, Robert’s team has found that this low, recommended application rate successfully kills a mound at least 95% of the time.
Robert’s team has also determined that the best time to apply a broadcast application of bait is in the fall. Fire ants are actively foraging for food during the mild temperatures of that season. As winter rolls in, the ants will move underground and slowly feed each other the pesticide that they took in from the broadcast granules.
If any of the colony remains and begins to emerge in spring, that’s the best time to apply bait directly on the mound. This one-two punch is a cost-effective way to make the most of any bait treatment, with minimal impact on beneficial garden creatures.
If, like me, you worry that birds or your backyard chickens will be harmed by toxic bait granules, remember that there are no truly and completely safe insecticides. That said, most products on the market have a low toxicity rate to birds, fowl or mammals.
Still, it’s best to take precautions. As Robert points out, every generation has proclaimed some product to be environmentally-safe – only to find later that it did cause harm. DDT is a perfect example. It was on the market for years, before its hazards became known.
This is why following an IPM model makes so much sense. It helps us to make focused, intentional and wise choices when it comes to pest management. IPM boils down to three crucial questions:
- Does the pest need to be controlled?
- Which control presents the lowest risk of unintended consequences?
- Does the benefit of application justify the risk of whatever control you are considering?
You might have heard that cornmeal is an effective fire ant treatment. Well, that one is a myth. The theory goes that, once a fire ant eats the dry grit, the granule swells inside the moist ant belly and – pop – ant firecracker. Now you know that theory fire ants can’t eat solid food. Instead, they’ll just carry the granules back to feed the colony larvae. Keep the cornmeal in the pantry, because it won’t do you any good against fire ants.
Whether you opt to treat or not, this problem isn’t going away for those of us in warmer regions of North America. Flying fire ant queens will reinvade spaces which have been cleared of bygone mounds. Fortunately for us, researchers like those at Texas A&M are still on the case to find a solution. If you listened to my recent podcast on the power of mushrooms, you’ve already heard that a fungal species may hold promise.
Be sure to listen in to this podcast too, by scrolling to the top of the page and clicking the Play icon in the green bar under the page title. Robert’s knowledge on the subject is not only interesting, but we shared some laughs too.
Links & Resources
joegardener Online Academy: Master Pests, Diseases and Weeds – my newest online course! Just $47 for lifetime access.