Fire ants are very effective predators because they reach very high densities and sting prey in large numbers. In the United states they prey on hatchling alligators, freshwater turtles, sea turtles and ground-nesting birds. Deer produce more young in places where fire ants are controlled, and the ants can remove 75 per cent of invertebrates from invaded land, leaving behind far fewer insects for hungry birds and lizards. They do harm both as predators and competitors, displacing other ant species over wide areas. In Australia one high-level report warned in 2016 that ‘iconic birds like the bush stone-curlew, plumed frogmouth, rufous scrub-bird, superb Iyrebird and black-throated finch are at significant risk,’ and it mentioned as well the tiger quoll and echidna, reptiles, frogs, freshwater fish and butterflies. Animals not killed outright can experience ‘reduced weight, loss of digits, obscured vision or blinding and an inability for normal movement’. The ants do not invade intact forest, but they will forage up to 40 metres from forest edges.
On American farms they do some good, consuming pesky insects and weed seeds and aerating soil, but their downsides are enormous. They tunnel inside fruits and prey on seeds, sometimes destroying whole crops. Potatoes, eggplants, sunflowers and citrus are some of the crops hit hard. They swarm over and punish farm workers, who receive penalty rates to contend with them, if they are willing to contend with them. The ants rob bee hives. They ruin sprinkler systems and hoses. Their mounds damage harvesting machinery. Worst of all, they attack newborn livestock, sometimes killing foals, calves and chickens. Sluggish or immobile animals are stung around the eyes and blinded. Farmers have to poison ants in pens where stock give birth. In the USA, the ants cost $US7 billion each year in impacts and control.
In the United States, which acquired them decades ago, other problems they cause include computer failures, fires, potholes, uninhabitable parks, crop losses, More than 80 people have died from the stings, mainly of anaphylactic shock. In nursing homes a growing problem is elderly patients killed in their beds. One woman died in a house fire after the ants caused a short circuit. Electrical currents attract them and when one is zapped the pheromones it releases attract its comrades, until the masses of dead bodies trigger failures of light switches, air conditioners, traffic lights, pumps, meters, even car electrical systems. Americans spend more than $6 billion a year on the problems they cause.
Modelling by the Queensland Government indicates that in southeast Queensland alone fire ants would impose costs of about $45 billion over 30 years. In Australia they could cause an extra 140,000 medical consultations and 3000 anaphylactic reactions a year.