Packing a Punch

The United States has become home to many unwanted insects that come to us from distant lands. Invasive species, as they are sometimes called, are notorious for becoming economically important pests. Several well-known examples can be found among the ants. In fact, two of the most well known ant pests, red imported fire ants and Argentine ants, were imported from South America and have become well established in our yards and kitchens where they vex homeowners and even pose a threat to human health.

Pachycondyla chinensis (Emery), native to Southeast Asia, was detected in the United States more than 70 years ago. In Japan the species is known as “oo-hari-ari,” which translates to “giant needle ant,” a name that describes the stout stinger capable of delivering a painful wound. The species does not have an official common name in the United States but we are proposing “Chinese needle ant,” a title that reflects both the native and the scientific names.

Until recently Chinese needle ants have been considered rare and have not been well recognized even by entomologists. We first came across these ants while doing research in the Great Smoky Mountains National Park. With a trip to the Museum of Comparative Zoology at Harvard University and the help of ant expert, Stefan Cover, the identity of this little-studied invasive species was confirmed. Armed with new knowledge and an eye for this species, it became obvious that northern South Carolina is teeming with these ants. Subsequently we started linking sting reports that came in through the Cooperative Extension Service and other sources to the Chinese needle ant. Typically when someone is stung by ants in the Southeast the sting is attributed to the red imported fire ant even without positive identification. It is likely that many more people have been stung by Chinese needle ants than have been reported or realized.

DESCRIPTION & RECOGNITION. Chinese needle ants have a caste system with adult ants serving as workers or reproductives. Workers and winged females are similar in appearance, while the male is strikingly different. Swarms of reproductive males and females might not happen at the same time and workers might not always be associated with them. So, it is important to recognize all the forms.

Chinese needle ants are medium-sized, single-node ants of the subfamily Ponerinae. The winged female reproductive is approximately 5.6 mm (0.22 inches) in length with a black body and brown legs and mouthparts. The smaller winged male is only 3.0 mm (0.12 inches) and is light brown to yellow in color. The male has a small head with relatively big eyes and long antennae. Workers are the most commonly encountered caste and can be recognized most easily by their size; about 3.5 mm (0.14 inches), slender build and black body with light brown mouthparts and legs. Unlike red imported fire ants and odorous house ants, Chinese needle ants don’t move quickly or erratically even when disturbed and can be characterized by their rather slow deliberate movement.

BIOLOGY & DISTRIBUTION. We have found Chinese needle ants nesting in forests — as well as urban areas — where they occupy dark and damp areas usually underneath objects resting on a soil surface. Chinese needle ants don’t nest in open sun-exposed areas like the red imported fire ant. Without turning over landscaping features such as railroad ties, concrete pavers or mulch, locating nests would be difficult as these ants do a good job of hiding the entrance. Nests that we have excavated have all been shallow, reaching maximum depths of 10 cm (4 inches) beneath the surface and contain from less than 100 to more than 5,000 individuals.

Typically colonies contain what appear to be multiple reproductive queens. Chinese needle ants are an ecologically dominant species that is able to compete with and possibly displace native beneficial species. In a Clemson forest, where we conducted detailed sampling of all ants, Chinese needle ants were the most numerous and second most common of 17 species making up the ant community. Chinese needle ants are now known in Alabama, Georgia, North Carolina, South Carolina, Virginia and Tennessee.

MEDICAL IMPORTANCE. The Chinese needle ant poses a threat to public health in the United States. Systemic allergic reactions to stings from Chinese needle ants can lead to anaphylaxis and cases have been well documented in Japan and South Korea. In 2006 a case of severe life-threatening anaphylaxis was documented in South Carolina. A survey of sting victims has shown that non-life-threatening symptoms may last for two hours to 14 days in the form of a painful itchy welt and localized swelling.

While not aggressively defensive of their nest, Chinese needle ants will sting humans in self defense when they become trapped next to skin. Typically this occurs underneath clothing or when ants are being brushed from an arm or leg. In early summer, when reproductive females are flying, the chances of being stung increase as females equipped with the same potent stinger as the workers are likely to land on unsuspecting people.

CONTROL STRATEGIES. Because experimental research will be required to develop an effective management plan for Chinese needle ants, our preliminary recommendations are based on our knowledge of the behavior of the species.

The first line of defense should be to ensure that flying reproductive females are not entering structures where they might sting people. The installation of tight-fitting screens and keeping bright lights away from open doors and windows should do the trick.

Secondly, conditions conducive to nest building should be addressed. Remove or minimize objects and mulch that could serve as cover for nests near problem structures. We recommend specifically targeting the nest, if chemical measures are warranted, to reduce populations. Nests should be relatively easy to locate and are shallow. Treat by moving natural and man-made objects resting on soil and drenching any galleries exposed. Individually placed baits may not be effective because Chinese needle ants do not recruit other colony members to a food source. Perimeter treatments in areas with high pressure and worker ants foraging inside structures might be effective because the ants do not nest indoors to our knowledge.

We do not know the range of Chinese needle ants in the U.S. and it appears the ants are spreading to new areas. They are likely to occur in most (if not all) of the Southeast. If you encounter black stinging ants that you don’t recognize, take the time to make a proper ID. You may have Chinese needle ants. With your identification and knowledge of control measures, you may be able to help your clients avoid a painful experience.

Eric Paysen is a graduate research assistant and Pat Zungoli and Eric Benson are professors in the Department of Entomology, Soils, and Plant Sciences at Clemson University in Clemson, S.C.