The southern United States looks headed for an ecological sea change --- not necessarily because of atmospheric warming or shifts in coastal ocean currents, but through the ongoing march of non-stinging Tawny crazy ants from South America.
Researchers from the University of Texas at Austin have concluded the forward migration of Tawny crazy ants through the country's southern region will likely wipe out the region's population of the dreaded red fire ant, which itself was imported to the states in 1930 and subsequently tore through the area ecosystem on its way to becoming one of the most dominating insect species around.
The study was published in a recent issue of the journal Biological Invasions.
The U.S. Food and Drug Administration estimates more than $5 billion has been is spent annually on medical treatment after red ant attacks, as well as, property damage control and prevention in fire ant-infested areas
It's also been estimated fire ants have caused approximately $750 million in damage annually to agricultural assets, including veterinarian bills and livestock loss, not to mention crop loss.
Those economic considerations, as bad as they've been, could grow even worse with the invasion of the crazy ants, according to the study's lead author, Ed LeBrun, a research associate with the Texas invasive species research program at the Brackenridge Field Laboratory in the College of Natural Sciences.
"When you talk to folks who live in the invaded areas, they tell you they want their fire ants back," said LeBrun. "Fire ants are in many ways very polite. They live in your yard. They form mounds and stay there, and they only interact with you if you step on their mound."
In contrast, said LeBrun, the "ecologically dominant" crazy ants "go everywhere."
The ants, for instance, can invade family's home, nest in crawl spaces and walls, become incredibly prolific and, as a result, damage electrical equipment.
The crazy ants were first discovered in the U.S. in 2002 by a pest control operator in a suburb of Houston, and have since established populations in 21 counties in Texas, 20 counties in Florida, and a few sites in southern Mississippi and southern Louisiana.
The UT researchers have studied two crazy ant invasion sites on the Texas Gulf Coast, finding that in those areas where the Tawny crazy ant population is densest, fire ants have been completely eliminated.
Even in regions where the crazy ant population is less dense, fire ant populations have been drastically reduced.
Other ant species, particularly native species, have also either been eliminated or greatly diminished.
LeBrun said crazy ants are much harder to control than fire ants, as they don't consume most of the poison baits that kill fire ant mounds and they don't have the same kinds of colony boundaries that fire ants do.
In other words, even if crazy ants are killed in a specific area, other crazy ants can combine into a supercolony that can well swarm back through a cleared area.
"They don't sting like fire ants do, but aside from that they are much bigger pests," said LeBrun. "There are videos on YouTube of people sweeping out dustpans full of these ants from their bathroom. You have to call pest control operators every three or four months just to keep the infestation under control. It's very expensive."
In northern Argentina and southern Brazil, where it's believed the ants originated, populations are held in check by other ant species and a variety of natural enemies, the study said.
In the U.S., however there is no such natural control --- which has allowed crazy ants to reach population densities of up to 100 times as great as all other ants in an area combined.
Aside from monopolizing food sources and starve out other species, crazy ants, which eat just about anything, may also directly attack and kill other ant and arthropod species, LeBrun said.
Ultimately, the crazy ants will cause a significant reduction in abundance and biodiversity at the base of the food chain, and that will impact the ecosystem as a whole.
"Perhaps the biggest deal is the displacement of the fire ant, which is the 300 pound gorilla in Texas ecosystems these days," said LeBrun. "The whole system has changed around fire ants. Things that can't tolerate fire ants are gone. Many that can have flourished. New things have come in. Now we are going to go through and whack the fire ants and put something in its place that has a very different biology. There are going to be a lot of changes that come from that."
LeBrun said a great deal about the Tawny crazy ants remains unknown, including their potential range. So far, most of the colonies are in fairly wet environments with mild winters, near the coast, so it may be the case that they can't thrive in drier or colder climates, and that fire ants will remain dominant in those areas.
But, he said, one thing about crazy ants in clear: "They are opportunistic nesters...they can take up residence in everything from a house plant, to an empty container left outside, to an RV. So they're easily transported."
So, if people living in or visiting invaded areas are careful and check for the crazy ants when moving or going on longer trips, they could have a huge impact on the spread of the ant population.
Cutting down on the number of potential transplantation events could slow the spread of crazy ants by years or decades, LeBrun said, and that extra time could give the ecosystem an opportunity to adapt and researchers more time to develop better controls.
"We can really make a difference," he said, "but we need to be careful, and we need to know more."
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