ANT SUPPLEMENT: Red Imported Fire Ants: A Fiery Foe

Fire ants are so named because their venom causes a burning sensation. And like fire, these pests are capable of blazing a costly and destructive path. Just ask residents of the southern United States, where red imported fire ants (RIFAs) now infest all or parts of 13 states.

"These are a non-native, invasive ant species with no naturally occurring enemies in the United States, which gives them a competitive edge over other ant species and insects," said Dr. Mac Horton, a professor and extension entomologist from Clemson University, Clemson, S.C. Horton discussed the biology, behavior and management of these economically significant and health-threatening pests at the PCT/Aventis Ant Symposium.

Although the black imported fire ant, Solenopsis richtieri, was first identified in the United States in 1918, the arrival of red imported fire ants, Solenopsis invicta, in the U.S. (in the1930s) has proven to be more significant. RIFAs are the more aggressive of the two species, and thus have been able to expand into new territories.

A SKILLED OPPONENT. Opportunities abound for PCOs who offer red imported fire ant control, but this type of work carries with it many challenges. Certain aspects of the biology and behavior of RIFAs are decidedly different than other pest ant species.

RIFA colonies produce virginal, winged reproductive males and queens in early spring, except in southern coastal states, where reproduction can be a year-round process. When weather conditions are right, they emerge, fly as high as 1,000 feet, and mate in the air. The male dies and the queen falls to the ground, loses her wings and starts a new colony. Mature fire ant colonies contain from 70,000 to 200,000 workers and a wide spectrum of different worker sizes. The majority are minor workers less than 1/8 inch long. The workers care for the queen and immature larvae and pupae defend and repair the nest (mound) and spend most of their lives foraging for food.

PCOs may receive more RIFA control requests when it rains. This is because RIFAs move horizontally and vertically in the soil profile to stay in a comfort zone. "People think (RIFAs) go away when it’s hot outside, but they actually will just go down in the soil profile to find a comfortable temperature and get humidity protection," Horton said. "They will come up again when it rains."

While fire ants are omnivorous to some degree and will eat both plant and animal material, they usually feed on other insects that they find and sting. The sting paralyzes the insect, which is then brought back to the mound if it is small enough. If it is too large for one ant to carry, more workers are recruited to cut up the insect into smaller pieces and take it back to the mound. The venom also acts as a preservative and inhibits decay in the food stored in the mound.

RIFAs are particularly attracted to plant oils, such as peanut and soybean oil. These oils are therefore used as attractants and as carriers for the insecticides used in fire ant baits. Note that oils used by fire ants as food are fed to the workers before they are fed to the queen. This renders fast-acting insecticides useless since workers are killed before they can feed the larvae and the queen. As long as the queen survives, the colony will continue.

A STINGING SENSATION. The major concern with red imported fire ants and what separates these ant species from others is the ability of its worker ants to sting. They inject a venom that causes blisters in both people and animals. These stings may cause severe allergic reactions and can even cause death in about 0.5 percent of people stung. Also, blisters that are broken can become infected and cause permanent scarring.

Although an individual RIFA sting does little damage, these pests attack in large numbers, stinging their victims simultaneously. "They have the ability to recognize that they need enough ants to make a difference when they are stinging, so a RIFA will find a food source, recruit other RIFAs, then they will locate the soft tissue and sting on command," Horton said. "In other words, by the time they start stinging they will have already covered their prey."

Red imported fire ants disrupt many outdoor activities, such as picnics and gardening. They seriously interfere with many farming activities such as mowing and bailing hay. Red imported fire ants also damage young seedlings and plants. They are attracted to electrical equipment, such as transformers, outlets, airport runway lights and even air conditioners, which they damage and cause to short out, sometimes resulting in fires. RIFAs have chewed through electrical cable insulation, resulting in shorts in telephone lines and traffic accidents.

CONTROL STRATEGIES. Because red imported fire ants can pose significant health threats in and around structures every effort must be made to control them. Efforts to control fire ants in the southeastern United States date back to 1937, when calcium cyanide was used against the black imported fire ant. In the 1960s, mirex was applied to millions of acres throughout South Carolina and other infested areas. Newer baits developed in the 1980s resulted in more environmentally acceptable, though more expensive, methods of control.

A number of different control methods can be used to eradicate fire ants, including: soil drenching, mound injections, fumigation, granular treatments and baiting. Of these methods, broadcast applications of fire ant baits are a popular choice, especially when eradicating fire ant problems from lawns and other large areas. Although broadcast baiting does not produce immediate eradication of fire ant mounds (the way mound injections do), it is a more thorough treatment. Broadcast baiting takes advantage of fire ants’ aggressive foraging behavior. The ants haul the bait granules back to their mounds and share it with their nestmates. It is also the most time efficient method if large areas need treatment.

Broadcast applications are also effective because they cover large areas and can treat mounds that are small and often overlooked. For example, although a mature mound in the middle of a field will be visible, new mounds and mature mounds that develop underneath structures such as paved sidewalks, will not be visible.

"Remember, for every mound you can see on the surface, there are two more hidden from view," Horton said.

Broadcast treatments are also less expensive (in terms of both time and money) and are more environmentally acceptable than other fire ant management strategies, Horton said.

It is critical to read a product’s label before making any RIFA broadcast bait application. These baits are normally applied at a 1 to 1½ pounds per acre rate, calculating to about ½ ounce per 1,000 square feet. Granular applicators capable of applying at such low rates are generally recommended for this type of application. Also, in infested areas larger than one acre, it is recommended at least two treatments be made (one in the fall and one in the spring) because these ants have the ability to reinfest.

WATCH OUT! Because young children and the elderly are the most susceptible groups to RIFA attacks, PCOs have to be extra careful when controlling RIFAs from schools and medical facilities. In most cases where fire ant stings severely harm individuals or cause death, the individual being stung was unable to move.

Horton has studied a number of legal cases in which pest control companies were sued by surviving family members of elderly medical patients who had died from RIFA stings suffered while they were hospitalized. PCOs will be sued because they were "the pest control experts," they had the knowledge that fire ants were close to a patient, they knew of the potential threats to a patient and they should have taken the necessary steps to remove the fire ants. Horton says that in the majority of those cases, the pest control companies had met the terms of the contract, practiced due diligence and otherwise fulfilled its obligations.

"But the pest control industry is very vulnerable from the standpoint of defending itself against fire ant lawsuits because of the time, energy and costs it takes to control fire ants," Horton said. "It’s my perspective that a fire ant infestation is an unpredictable event and can occur no matter how good a job you are doing in the immediate vicinity."

To protect oneself from fire ant lawsuits Horton advises PCOs to practice due diligence, keep an eye out for fire ants at all accounts (even when they are not on the contract) and not guaranteeing 100 percent control of fire ants.

CONCLUSION. Since their arrival in United States in the 1950s, red imported fire ants have been a serious health pest and a growing problem throughout many parts of the country. Because RIFAs are spreading to new areas, many PCOs are now performing fire ant control services for the first time.

While this line of work may be exciting and profitable, it also has certain unique challenges. For pest management professionals to be successful in the management of RIFAs, they must not only be knowledgeable about the biology and behavior of these pests — they must also have a thorough understanding of the proper products and treatment procedures.

The author is managing editor of PCT magazine and can be reached at bharbison@pctonline.com