Bug of the Month: Imported Red Fire Ants
By: Sarah Adams
Member of the Big Country Master Gardeners
This month’s bug is the Red Fire Ants. I was saddened to find three very large fire ant mounds in 3 of the 4 corners of just one of my raised vegetable beds. These fire ants make it terribly difficult to work in the garden.
Imported red fire ants are in the Animal Kingdom, Phylum Arthropoda, Class Insecta, and the Order Hymenopteran, Family Formicidae, Genus Solenopsis, Species invicta. Fire ants are a significant ecological and economic concern in Texas since their introduction in the 1930s. The imported red fire ant is native to South America but has become a notorious invasive species in many parts of the world, including Texas. Since their accidental introduction to the United States through the port of Mobile, Alabama, in the 1930s, imported red fire ants have rapidly spread across the southern United States. Their aggressive behavior, ability to outcompete native species, and painful sting have earned them an infamous reputation, causing significant ecological and economic damage.
The first documented introduction of imported red fire ants in Texas occurred in the late 1950s. Since then, the species has spread rapidly, infesting approximately 26 million hectares of land in the state by 2022. The spread of red fire ants in Texas has been facilitated by human activities such as transportation of infested soil and plant material, as well as natural dispersal mechanisms. Their ability to thrive in a wide range of habitats, including urban, agricultural, and natural ecosystems, has further contributed to their successful establishment.
Imported red fire ants have profound ecological impacts as they outcompete native ant species for resources, disrupt ecosystems through predation and competition, and alter soil structure and nutrient cycling. Their aggressive behavior also poses a threat to small vertebrates, ground-nesting birds, and other invertebrates. Additionally, red fire ants can indirectly affect ecosystem dynamics by altering plant-pollinator interactions and seed dispersal patterns.
Given the significant problems that fire ants cause, there is a strong desire to kill them in our gardens. However, as we have discussed in prior articles, if you use pesticides in the garden to kill the ants, then you are destined to kill other beneficial insects disrupting the delicate balance of bugs in our gardens including the pollinators that we spend time and resources trying to attract to our garden. However, something must be done to control these ants or it can prohibit gardeners from being able to garden. So, what do we do?
One option is to pour 1-2 gallons of very hot to boiling water on these fire ant mounds. This is not particularly effective but it is a start. The method has been shown to kill 60% of fresh first ant colonies. This obviously has its downsides in that one must handle a large amount of water capable of burning one’s skin and it may kill the plants if enough hot water seeps into the plant. However, if you keep a good eye on the garden and see a brand-new mound pop up then it might be worth a try.
Another method is to plant herbs with natural compounds to repel ants like lavender, eucalyptus, thyme, and mint. These strong scents are said to deter ants from foraging for food in the area that they are planted. I have had exactly zero success with this method, but that doesn’t mean that it won’t work for another gardener in a different garden.
Another option is to try Diatomaceous Earth – commonly known as DE. A gardener would need to purchase food grade DE for use in the vegetable garden. DE is made from ground-up bodies of prehistoric diatomic fossils. When well ground DE has a very sharp consistency that has the effect of miniature razor blades which can destroy the mucous membranes of breath holes and lungs in bugs. It can also dry out and scrape off any outside membranes of a bug. This treatment can harm bees as well, so if using this method take care to not use while the plants are flowering or cover treated areas so that helpful bugs aren’t affected by the DE.
The only commercial product that is recommended by AgriLife Extension for use in an edible garden is the Ferti-lome Come and Get it. It is an ant bait that attracts foraging fire ants and allows these ants to take the poison back into the nest as food for the colony. Ant baits are commercially available and come in liquid, granular, and gel form. They are different than ant sprays because the chemical does not kill the ant on contact; rather the chemical is brought back into the mound so that the ants will eat the bait and die. It is stated that dead ants can be seen as quickly as 24 – 26 hours after application. The active ingredient is Spinosad which affects the nervous system of insects that eat or touch it. According to the National Pesticide Information Center, spinosad causes their muscles to flex uncontrollably. This leads to paralysis and ultimately their death, typically within 1-2 days. Spinosad is broken down rapidly by sunlight. In the presence of sunlight, half-lives on leaves are 2 to 16 days and less than one day in water. When applied to leaves, some spinosad can be absorbed. However, it does not readily spread from leaves to the rest of the plant. In the absence of sunlight, spinosad breaks down very slowly in water. Half-lives of more than 30 days to 259 days have been reported. However, it binds rapidly to sediment. The half-life in sediment, where no oxygen is available, ranges from 161 to 250 days. Spinosad also sticks to soil and has a very low potential to move through soil towards ground water. In field studies, no break down products of spinosad were found below a soil depth of two feet. In the top layers of soil, spinosad is rapidly broken down by microbes. Soil half-lives of 9 to 17 days have been reported. After it is applied, spinosad is not likely to become airborne. I have used this product for years and it works for the season, but the ants come back constantly. So, this is a routine maintenance product for my garden. Basically, the mound leaves – I think it just moves – until it decides to move again and then because my garden is full of aeriated, organic soil the ants find their way back to the garden and I start over. See https://liberty.agrilife.org/files/2020/06/Managing-Fire-Ants-in-Vegetable-Gardens-Publ.-Ento-015.pdf
There are several effective products for use in one’s yard and outside the vegetable garden. AgriLife recommends the Texas Two-Step. Step 1, bait the area with fresh baits, usually a granular product that is simply sprinkled on and near the mound. Apply the baits when the ground is dry and no rain is expected. Step 2, follow the product directions for individual mound treatments. These are chemical treatments and are not approved for the vegetable garden, but they are quite effective for lawns and other non-edible garden beds. See https://fireant.tamu.edu/materials/videos/
If you have any questions, call the Taylor County Extension Office at 325-672-6048 or email us at mgardeners@yahoo.com. We hope you visit bcmgtx.org for information on all Big Country Master Gardener events, like us on BCMGA Facebook, and check out training presentations on BCMGA YouTube. We are here to help you.
