Invasive Crazy Ants Displace Fire Ants as They Invade the Southeast

No one likes fire ants, but "crazy ants" don't sound very appealing, either. Now, researchers have announced that invasive "crazy ants" are displacing other species in areas across the southeastern United States.

Crazy ants are ecologically dominant, and are currently reducing diversity across a range of ant and arthropod species. First discovered in the U.S. in 2002 in Houston, they have since spread out to 21 counties in Texas, 20 counties in Florida and a few sites in southern Mississippi and Louisiana. Yet it wasn't until 2012 that the species was formally identified as Nylanderia fulva, which is native to northern Argentina and southern Brazil. It's commonly known as the Tawny crazy ant.

The invasion of crazy ants, though, is just the latest in a string of invasive ant species. The fire ant was actually first introduced around the 1930s and displaced native ant species. With the ability to cause painful stings, this particular ant isn't the most beloved of pests.

Crazy ants may be even worse than fire ants, though. The ants go everywhere. They invade homes, nest in crawl spaces and walls and can even damage electrical equipment. They're also much harder to control than fire ants since they don't consume most of the poison baits that are used to kill fire ant mounds. In addition, they don't have the same kinds of colony boundaries that fire ants do; this means that even if they're killed in a certain area, the supercolony survives and can swarm back over the area.

"They don't sting like fire ants do, but aside from that they are much bigger pests," said Ed LeBrun, a research associate with the Texas invasive species research program, in a news release. "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 order to examine exactly how far crazy ants have spread and how they might affect local species, researchers studied two crazy ant invasion sites on the Texas Gulf Coast. They found that where the Tawny crazy ant population is densest, fire ants were eliminated. In fact, even where crazy ant populations were less dense, fire ant populations were drastically reduced. Other ant species, including native species, were also eliminated or diminished.

The ability to displace fire ants is a huge deal in the insect world. Fire ants were previously the dominant invasive ant species in ecosystems. The fact that they're now being displaced by crazy ants could mean some drastic changes are in order.

"Perhaps the biggest deal is the displacement of the fire ant, which is the 300 pound gorilla in Texas ecosystems these days," said Le Brun. "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."

Currently, researchers plan to continue studying crazy ants. However, they point out that it's important to help cut down on their spread. Keeping transplantation events to a minimum could slow down the extent of their range in the U.S. by years or decades.

The findings are published in the journal Biological Invasions.