Meet an unwelcome visitor from Central America that has been stinging residents of the Deep South for years—yet going virtually undetected by science. It might be unwelcome, but it seems to relish it here, and researchers warn that it is spreading rapidly.
Odontomachus haematodus is a bellicose variety of trap-jaw ant, with some specimens approaching half an inch in length. The United States is home to native trap jaw ants, but they are small and timid compared to their invading counterpart. The natives tend to flee when their nest is disturbed. But O. haematodus will lash out with its portly mandibles—which are also used to mash up competitors and prey, and to spring themselves away from would-be predators.
"I had my hand down to look for ants in the leaf litter and I was immediately stung," says Joe MacGown, a Mississippi Entomological Museum researcher who has spent more than a decade sampling and studying ants along the Gulf Coast. "They're aggressive—and they have a potent sting."
MacGown analyzed museum collections and discovered three O. haematodus specimens that had been collected during a field study in Mobile, Alabama, in the summer of 1956. It's not known whether those specimens represented a failed colonization of the U.S., or whether their colonies helped seed the colonies that have suddenly become widespread in some areas of southern Alabama, northern Florida, southern Mississippi, and Louisiana. Either way, a team of scientists, which included MacGown, studied the abundance of six invasive trap jaw species and concluded that O. haematodus and another invasive variety are rapidly expanding their Gulf Coast territories—threatening residents and wildlife alike.
"It is clear from collecting records that the abundance of O. haematodus along the Gulf Coast is a recent phenomenon, and it is also clear that this species is continuing to spread."
"I think this species has already negatively impacted native species," MacGown says. "Typically, one would expect to find numerous colonies of various species of carpenter ants and Aphaenogaster [myrmicine ants] nesting in rotting logs and other wood, in hollow trees, in leaf litter at tree bases, and other similar microhabitats. But where the O. haematodus is now common, it's difficult to find those species."
The colonies range from a few hundred ants up to thousands of workers and multiple queens. They are being discovered in dunes, forests, savannas, along the banks of estuaries, in yards, under mulch, in trees and rotting stumps, among plant roots, in building foundations, and tucked beneath PVC pipes. The species has become a major pest at the Audubon Zoo in New Orleans.
"It is clear from collecting records that the abundance of O. haematodus along the Gulf Coast is a recent phenomenon, and it is also clear that this species is continuing to spread," the researchers write in a paper published recently in Zootaxa.
MacGown says residents have complained to him about the ants for years, sharing stories of ants jumping and landing multiple stings. But he says a lack of entomological expertise and interest in the region means we still know very little about what types of threats they might pose, or what we could do about them.