Alien ‘crazy ants’ invading southern U.S.

An illustration shows the tawny crazy ant, a South American invasive species that first was found in Texas in 2002 and since has spread to at least three other Gulf Coast states.
(Joe MacGown / Mississippi Entomological Museum)

An invasion of alien “crazy ants” is making many residents of the U.S. Gulf Coast long for the old days of pesky, biting fire ants.

Like fire ants, these South American invaders seem to be fond of electrical equipment. But unlike their stinging red counterparts, the tawny crazy ants create mega-colonies, sometimes in homes, and push out local populations of ants and arthropods, a University of Texas researcher warns.

Here’s a bit of the behavior that earns the “crazy ant” name.

“When you talk to folks who live in the invaded areas, they tell you they want their fire ants back,” said Ed LeBrun, a researcher at the University of Texas’ invasive species research program. “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.”


Native to northern Argentina and southern Brazil, tawny crazy ants, or Nylanderia fulva, were discovered in a Houston suburb by a pest control worker in 2002. Populations since have fanned out through Texas and the Gulf Coast region as far as Florida, where 20 counties have active colonies, according to LeBrun, who published a study of the invasion in the aptly named journal Biological Invasions.

LeBrun believes the ants came to the U.S. through the Port of New Orleans. That’s how the Argentine ant got here in 1891; the black fire ant was first found near the port of Mobile, Ala., in 1918, and in the 1930s, the well-known and despised red fire ant showed up, pushing out the black fire and Argentine ants.

The ants’ habit of colonial dominance worries researchers. Super-colonies of the newcomers have eliminated the local populations of five other species, including red fire ants, in areas of the Texas Gulf coast, the researchers found. In areas where crazy ants haven’t gone quite as crazy, populations of other ants are in decline.

Thus far, the crazy ants are not falling for the traditional poisons used to eliminate fire ant mounds. And when local mounds are destroyed manually, they are quickly regenerated.

“They don’t sting like fire ants do, but aside from that they are much bigger pests,” LeBrun said. “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.”

Colonies in the South appear to have no natural predators. So colonies can grow to be 100 times the size of those of local ants, which can’t compete for food sources. The crazy ants also directly attack local populations.

How the decreased biodiversity will affect the overall ecosystem remains unknown. Also unknown is the range of the ant, which thus far seems to thrive in wet environments with warm winters.

Any spread will be somewhat slower than that of other species because the reproductive members of crazy ant colonies don’t fly. Colonies advance about an eighth of a mile a year - unless they hitch rides, as they have been known to do, in nursery plants, or even in recreational vehicles.