Brachymyrmex patagonicus

Introduced to North America, Spain and Hong Kong from South America, this invasive ant can be a pest in its introduced range. It appears to thrive in disturbed habitats in both its native and introduced ranges.

Identification
MacGown et al. (2007) - In the United States, B. patagonicus is most similar to Brachymyrmex obscurior, another exotic species. Workers differ in the size of the eye, which is about the length of the malar space in B. patagonicus, and conspicuously shorter than the malar space in B. obscurior. Additionally, the gaster of B. patagonicus has scattered pubescence, giving it a more shiny appearance, whereas B. obscurior has more dense pubescence. An undescribed species of  Brachymyrmex recorded from Florida (referred to as Brachymyrmex brevicornis Emery in some publications-Deyrup 2003; Deyrup et al. 2000) is also dark brown in color, but lacks erect hairs on the body. Another undescribed, brown colored species, known only from 2 queens from Arkansas, differs from B. patagonicus in that the queens are tiny, approximately the size of typical workers (pers. comm., Lloyd Davis). Brachymyrmex heeri Forel is another similar species that could be potentially found in the United States, but has not been found here yet. Workers of this species are brownish-yellow and lack ocelli. Other species of Brachymyrmex found in the United States are yellowish in color.

Distribution based on Regional Taxon Lists
Nearctic Region: United States. Neotropical Region: Argentina, Brazil, Paraguay. Palaearctic Region: Spain.

Biology
MacGown et al. (2007) - This species nests in a variety of habitats, both natural and disturbed. Natural habitats include pine forests (with nests often in loose bark at the bases of the tree trunks), beaches (with nests at the bases of plants), mixed forests (nests in soil, dead wood, and litter), and prairie remnants (nests in soil, accumulations of organic litter, and grass thatch). In disturbed areas, nests of B. patagonicus are especially frequent in landscaping mulch, a habitat that is increasing exponentially throughout the Southeast, and which positions colonies to make forays into buildings. In disturbed areas it also nests in soil under objects on the ground (stones, bricks, railroad ties, lumbers, or a variety of other objects), under grass at edges of lawns and parking lots, in leaf litter, at the bases of trees, in rotting wood, in piles of dead wood, and in accumulations of trash. Colonies may contain many hundreds of workers packed into a small sheltered area. Where this species is found, colonies are often abundant and even may be found within a few centimeters from one another. The social structure of B. patagonicus has not been studied, but apparently separate colonies show considerable mutual tolerance.

In many sites the occurrence of B. patagonicus appears to be centered around urban areas or places frequented by people, such as the more intensive recreation areas of state parks, gas stations, restaurants, grocery stores, and along highway edges. As is the case with many other pest plants and animals, this species appears to act as an invasive organism that is likely to return quickly whenever there are attempts to control it or other species of ants. It has been reported that this species may be found in higher numbers after imported fire ant suppression has taken place (Dash et al. 2005). This does not imply that populations of this species are excluded in areas where large populations of fire ants are present, as recent surveys of ants in the Southeast by the MEM have found this species to be abundant in areas with high numbers of imported fire ants. We have observed this species nesting side-by-side and freely roaming about with both Solenopsis invicta and S. invicta × richteri on numerous occasions and have seen no obvious correlation of its abundance to that of the fire ants’ presence and abundance.

This species is considered a nuisance pest species, as both alates and foraging workers may enter houses, hospitals, schools, or other man-made structures to forage and/or nest. Occasionally these infestations may be quite large, with nests being found in the structure of the buildings, especially in bathrooms and kitchens, in light sockets and in electrical outlets, inside cinder blocks of exterior walls, and under shingles. During recent years (2005-2006), the Department of Entomology and Plant Pathology at Mississippi State University has had more requests by pest control operators in Mississippi about this species than all other ant species totaled together. Pest control operators have found this species in very high numbers in hospitals and other businesses, especially in metropolitan areas, and have expressed difficulty in controlling it. This may be partly due to the fact that many indoor infestations of foraging workers may be coming from outdoor nests some distance from control efforts. As in the case of B. obscurior and other ants whose alates fly into openings in buildings or clutter up swimming pools, there may be no effective control of alate patagonicus where the ambient population is high, except by restricting access. The attention received by this ant may be more associated with its novelty than with any harm it causes, as it does not cause structural damage, bite, sting, or transmit disease, nor has it been shown to invade stored foods. As a nuisance species, however, invading buildings and causing annoyance, patagonicus shows considerable potential, perhaps comparable to the effects of Tapinoma melanocephalum in tropical and subtropical regions.

The diet of Brachymyrmex patagonicus is thought to consist largely of honeydew from various insects, especially subterranean homopterans (Dash et al. 2005). They undoubtably supplement their diet with other food sources and will readily come to sweet baits such as honey or cookies. Workers of these ants can be commonly seen scurrying about during the day as they forage. Female and male alates have been collected from mid May through early Aug.

Presence in United States
MacGown et al. (2007) - Although B. patagonicus is a relatively recent introduction to the United States, it is now well established and abundant in both natural and disturbed areas throughout much of the Southeast, especially in Georgia, Florida, Alabama, Mississippi, and Louisiana. To give an indication of how common B. patagonicus is within its range is the fact that the authors have usually been able to find workers of this species at new localities within 5 minutes by simply stopping at gas stations, motels, restaurants, and other such businesses, and searching at the edges of parking lots, at edges of grass areas, on tree trunks, exteriors walls of buildings, or on bare ground. Random stops at highways and rural roadsides have revealed similar abundance and ease of detecting this species.

A major reason for the success of B. patagonicus in the United States may be its ability to thrive in a variety of habitats, especially disturbed sites. Other contributing factors could be its ability to coexist with a variety of other dominant ant species, such as Dorymyrmex bureni, S. invicta, Pheidole moerens, and Pheidole obscurithorax. This is similar to other species of Brachymyrmex, which also usually occur where there are many other ant species that are larger, faster, more hard-bodied, and armed with stingers and more powerful mandibles. It is difficult to avoid the conclusion that this species may be protected by potent chemicals.

Because colonies can fit into a small space, they easily could be transported by man from site to site, making it likely that this species will increase its range further.

It is unclear what affect, if any, this species will have on native species in the area, but based on its abundance where it is now established, it might have some negative impact.

Presence in Hong Kong
Guenard (2018) - The collecting site in Hong Kong is located at the tip of a zone of reclaimed land and heavily urbanized. The specimens were first observed foraging at the base of two planted Araucaria heterophylla (Salisb.), an introduced tree species within a landscaped urban habitat. Foraging activities were observed on December 11th in the morning at 8:45am and around 10:30am. At the time of the initial observation, atmospheric temperature was close to 17°C, and while the bark surface was directly exposed to the sun, constant wind likely cooled the surface. On the afternoon of December 16th (3 to 4:30pm), additional sampling was performed using baits (cookie crumbs) to collect more workers and other species in the vicinity. Over 60 workers of B. patagonicus were observed, including a few meters away from the original sites (within a radius of 5m) on bare ground and lawn. A few individuals were observed at collecting baits, however no mass-recruitment was observed despite the high ground temperature measured (22.7°C to 25.8°C). While workers were observed using a similar trail suggesting the potential use of pheromonal communication, the density of workers observed was low. Three other ant species were observed in the same area, Pheidole megacephala which appeared dominant on baits, and more rarely Paraparatrechina sauteri and Cardiocondyla minutior; the latter is here recorded for the first time in Hong Kong as well and was recently collected from the nearby territory of Macao (Leong et al. 2017). The presence of B. patagonicus at the basis of a coniferous species is worth noting as the association of this ant with pine trees has been reported previously in its North American introduced range (MacGown et al. 2007, Hill 2017) as well as in its native range in association with exotic pine trees in Patagonia (Corley et al. 2006). The presence of B. patagonicus within landscaped habitat and heavily urbanized environment is similar to observations in collecting sites in other introduced regions such as southern Spain (Espadaler & Pradera 2016), or North Carolina, USA (North Carolina State University Campus: Guénard et al. 2014).

Chemical Ecology
LeBrun et al. (2015) found a behaviour, first noted and resulting from interactions between Solenopsis invicta and Nylanderia fulva, that detoxifies fire ant venom is expressed widely across ants in the subfamily Formicinae. This behavior was also studied and shown in experiments with B. patagonicus. See the biology section of the N. fulva page for a description of acidopore grooming and the use of formic acid for detoxification of a specific class of venoms that are produced by ants that may interact with formicines in the context of predation and food competition.

Nomenclature

 *  patagonicus. Brachymyrmex patagonicus Mayr, 1868b: 164 (w.m.) ARGENTINA. Emery, 1906c: 179 (q.). Senior synonym of atratula: Quirán, et al. 2004: 275.
 * atratula. Brachymyrmex patagonicus var. atratula Santschi, 1923b: 657, fig. 3 (w.) ARGENTINA. Junior synonym of patagonicus: Quirán, et al. 2004: 275.

Worker
MacGown et al. (2007) - Size minute, mesosomal length 0.43-0.51 mm (n = 10). Head and mesosoma medium brown to blackish-brown, gaster usually blackish-brown, often darker than head and mesosoma, tarsi and mandibles pale, and antennae brownish-yellow. Head slightly longer than wide, covered with fine pubescence, and with a few longer erect hairs; antennal scapes surpassing occipital border of head by 1/5 their total length; eyes relatively large, about as long as length of malar space and placed at approximately the middle third of side of head; 3 tiny, barely visible ocelli present. Promesonotum with 3-9 (usually 4-6) stout, erect hairs present dorsally, with fine pubescence that does not obscure the shiny sheen of integument. Gaster with scattered, long, erect hairs, especially along the edges of the tergites, and with sparse, decumbent hairs, separated by about 1/3 to 2/3 their length.

Queen
MacGown et al. (2007) - Mesosomal length 1.24-1.42 mm (n = 10). Concolorous light brown. Head wider than long, with abundant, fine pubescence, and with long erect hairs present; large compound eyes located at middle of side of head; 3 large ocelli present; frontal lobes well developed; scapes surpassing occipital border by 1/4 their length. Mesosoma with moderately dense, fine pubescence, and 30-40 long erect hairs (about 3-4 times length of fine pubescence); anepisternum and katepisternum separated by a distinct suture, with erect hairs present. Forewing with pterostigma; hind wing with 7 hammuli. Gaster with moderately dense, fine pubescence, and erect hairs along apical edges of sternites and tergites.

Male
MacGown et al. (2007) - Mesosomal length 0.8 mm (n = 2). Head dark brown to blackish-brown, rest of body, including appendages, very light brown. Head wider than long, with fine, sparse pubescence, lacking erect hairs except on mouthparts, and with smooth, shiny integument; frontal lobes reduced; scapes surpassing occipital border by more than 1/5 their length, first segment of funiculus enlarged, almost globular, wider than succeeding segments; eyes large, about 1/2 length of head, and located on lower half of head; 3 large, prominent, raised ocelli present. Mesosoma with sparse pubescence and shiny integument, lacking erect hairs. Hind wing with 5 or 6 hammuli. Gaster shiny, lacking pubescence, with scattered erect hairs on last few sternites and tergites.