Brachymyrmex patagonicus is the type species of the genus, and is a small, shiny, light brown to dark brown species with reduced pilosity. The original type material used by Mayr (1868)to describe the B. patagonicus cannot be located, prompting the species to be redescribed based on Chilean material also examined and determined by Mayr (Quirán et al., 2004). The redescription was part of a larger effort to clear up the confusion surrounding Brachymyrmex taxonomy (Quirán, 2005;2007), but several errors concerning the erroneously small size of the workers and queens of B. patagonicus were also published (MacGown et al., 2007). Brachymyrmex patagonicus is native to at least the South America region of the Neotropics (Quirán et al., 2004), and is introduced to the Southeastern United States (MacGown et al., 2007), and at least the Netherlands in Europe (Boer & Vierbergen, 2008). A review of B. patagonicus as an emerging pest species in the Gulf Coast region of the United States provides a thorough account of the taxonomy, invasion history and biology (MacGown et al., 2007). The authors suggest that B. patagonicus shows considerable potential as a nuisance species; perhaps comparable to the effects Tapinoma melanocephalum has in tropical and subtropical regions.
The first record B. patagonicus in the United states, from Louisiana in 1978, was misidentified as B. musculus (Wheeler & Wheeler, 1978). The species continued to be referred to under that name in publications, including subsequent faunal lists for Florida (Deyrup, 2003; Deyrup et al., 2000), until MacGown et al. (2007)determined that all records of B. musculus in the region in fact referred to B. patagonicus.
The diet of B. patagonicus is thought to consist largely of honeydew harvested from a diversity of insects, especially subterranean hemipterans (Dash et al., 2005), and are attracted to sweet baits such as honey or cookies (MacGown et al., 2007). The species nests in a variety of both natural and disturbed habitats. Natural habitats reported from MacGown et al. (2007)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 of B. patagonicus may contain many hundreds of workers packed into a small sheltered area, and colonies are often abundant and may be found within a few centimeters from one another (MacGown et al., 2007). The social structure of B. patagonicus has not been studied, but apparently separate colonies show considerable mutual tolerance (MacGown et al., 2007). Although it has been reported that B. patagonicus may be found in higher numbers subsequent to the suppression of Solenopsis invicta (Dash, 2004), the species is also known to coexist with both S. invicta and S. invicta x S. richteri (MacGown et al., 2007).
Brachymyrmex patagonicus is considered a nuisance pest, primarily because altaes and foraging workers may enter houses, hospitals, schools and other man-made structures to forage and/or nest (MacGown et al., 2007). The species can occur in very high numbers, especially in metropolitan areas, and pest control operators have expressed difficulty controlling it. However, there are no reports thus far of B. patagonicus causing structural damage, bites or stings, transmitting disease, nor invading food stores.
Diagnosis among workers of introduced and commonly intercepted species in the United States. Antenna 9-segmented. Antennal club indistinct. Antennal scapes surpassing the posterior margin of head by more than 1/5th their length. Eyes of moderate size (greater than 6 facets). Eye length approximately equal to malar distance. Head with or without distinct ocelli. Antennal sockets and posterior clypeal margin separated by a distance less than the minimum width of antennal scape. Dorsum of mesosoma lacking a deep and broad concavity. Metanotal groove present. Pronotum and mesonotum with pairs of erect hairs. Propodeum and petiolar node both lacking a pair of short teeth. Propodeum lacking posteriorly projecting protrusion. Metapleuron with a distinct gland orifice. Waist 1-segmented (may be hidden by gaster). Petiolar node appearing flattened. Gaster armed with acidopore. Gaster (especially first segment) with sparse pilosity, giving it a shiny appearance. Color dull brown.
Brachymyrmex patagonicus can be distinguished from most other introduced members of the genus by the following combination of characters: (1) sparse pubescence on the first gastral tergite, (2) antennal scapes exceeding posterior margin of head by at least 1/5 their length, (3) erect hairs on the pronotum and mesonotum, (4) eye length approximately equal to malar length, and (5) shiny brown in color. In North America, the species is most readily confused with B. obscurior, but can be separated by the sparser pilosity on the gaster and the larger eyes.
Brachymyrmex obscurior
Native Range (Quirán et al., 2004): Argentina, Paraguay, Bolivia, Brasil (RS, SP, RJ, AM), Guianas, Venezuela.
Introduced Range. Netherlands. USA: Arizona, Alabama, Georgia, Florida, Louisiana, Mississippi, Missouri, Texas.