There are many things I’ve learned since moving from garden design and landscape planting into sustainable farming. The most obvious is that controlling insects and disease using organic methods is extremely difficult in southern Georgia. Mild winter temperatures allow for the successful overwintering of many species. As each year has gone by, pests have multiplied their numbers so that growing vegetables is an ever-increasing challenge. There are often moments that I feel they are winning the battle.
If someone were to ask which is the most persistent problem, I would have to say fire ants. I only knew two things about these aggressive little critters from my landscape design days-they tend to live in large colonies and it’s best to stay clear of any sign of them. Here’s what I know now.
Fire ants are members of the order Hymenoptera, which includes wasps and bees. The fire ant genus, Solenopsis, contains 280 species that can be found around the world. Out of all of these, one species, the red imported fire ant, (Solenopsis invicta) has had a huge impact since its accidental introduction into the United States sometime in the late 1930s. This exotic invasive species, native to Brazil, accidentally arrived via a cargo boat. Unfortunately, it never left.
Fire ants are social creatures. They live in large colonies consisting of one queen (monogyny) or multiple queens (polygyny). The queens are the only egg-layers and are the largest ants. They will lay fertilized eggs that will develop into sterile unwinged female worker ants, into fertile winged females or into winged males. Males are short lived; after emerging and mating with a winged female, they die. The winged female, storing the male sperm inside her body, will then drop her wings and become a queen starting her own colony. Worker ants, hatching from fertilized eggs laid by the queen, will number into the 200,000’s inside the colony. They look for food, care for the young, and defend the nest. They build a series of underground tunnels that can extend up to 25 feet away from the mound. Often times a large mound is not formed above ground unless the ants are fighting colder temperatures or heavy rains.
Fire ants are aggressive. If a colony has one queen, that colony limits the number of other colonies in the vicinity to about 150 colonies and 7 million ants per acre. However, if a colony has more than one queen, the colony may allow up to 300 colonies and 40 million ants per acre, not only tolerating them but also sharing resources among the colonies. The aggressive nature of fire ants keeps local ant competition to a minimum and can effectively drive other insects to extinction.
Fire ants are resilient. When floodwaters rise, they will latch together to form a floating boat, with the queen perched on top. They can float for a very long time, with the worker ants below water rotating positions with those above water until dry land is reached. In hot, dry conditions and in cold temperatures, the colony moves deeper into the ground for protection. In very cold winters, up to 80-90 percent of the colony will die. However, if the queen survives, she only needs a half-dozen workers to reestablish the numbers in a short amount of time. (Note: Because of their susceptibility to extreme cold, fire ants are generally found in the southern states).
Fire ants are omnivores. They eat insects, seeds, fruits, plant nectar and honey dew excretions from other insects. They also feed on invertebrates and vertebrates including reptiles, birds and mammals. They are particularly attracted to sweets and fatty substances.
ants both bite and sting. First, they clamp down with their mandibles to get a firm grip on their victim, then sting with the stinger located on the end of their abdomen. When they sting, they inject an alkaloid venom, solenopsin. Stings can actually result in death if a large number occur. A human who is highly allergic to the venom should seek immediate medical attention. And yes, a disturbed colony member will release a very volatile alarm pheromone that acts quickly on nearby ants so that they sting all at the same time. They can sting multiple times. The attack is painful, feeling like a tiny burst of fire and eventually forming a white pustule at the site. The wound site also itches. In my case, sometimes it leaves a small brown scar particularly when it becomes infected (because I pick at it or scratch it).
Fire ants defend (tend) members of the order Homoptera. Aphids, leafhoppers, and mealybugs all benefit from the protection by fire ants from predators. The fire ants feed on the sugary honeydew excretions. This relationship is termed mutualistic.
Fire ants can be controlled, not completely eliminated. For serious control on turf and non-agricultural lands, apply bait at a rate of 1 to 1-1/2 pounds per acre with a broadcast spreader, using milorganite as the carrier rather than sand. Broadcast in the spring when temperatures are in the mid-70s for at least three days in a row. Follow with a second application when those same temperatures occur in the fall. Apply bait in the early morning just after the dew is gone from the grass, with no rain in the forecast or irrigation running. It needs a dry period of a minimum of 24 hours, preferably 48. Unfortunately, this method of control is not permitted in an organic garden or in vegetable gardens. I have applied bait to the perimeter of the garden to keep fire ants from moving in and have tried the old-fashioned method of pouring 1-3 gallons of boiling water on mounds after a rainfall or on a cool sunny morning when ants are near the surface. I have also used organic botanical insecticides containing pyrethrin or spinosad. The limited success I have had is based on my diligence and perseverance. I admit I tend to treat the areas where I am attacked most frequently and ignore the many other colonies present in further reaches of the garden. This somewhat lackadaisical method is not recommended. Sadly, one look at my ankles and hands is proof. If only I didn’t have to till, plant, weed and control other disease and pest problems, I just might get the upper hand!