by Joe A. MacGown, uploaded 3 November, last updated on 25 November 2013
Brachymyrmex patagonicus, full face view of a worker
Photo courtesy of http://www.antweb.org/.
Brachymyrmex patagonicus is a small dark brown species with pale tarsi and mandibles and brownish-yellow antennae. The promesonotum usually has at least four erect hairs. The gaster has sparse, but rather long pubescence. The head is slightly wider than long. The eyes are relatively large; about as long as the length of the malar space. Minute ocelli are lacking, but some large setal sockets may give the impression of ocelli. The scape obviously surpasses the occipital border.
A word of caution, this group is in need of revision. This particular species has been identified as both B. musculus Forel and B. patagonicus for the last 30 years since it was first reported to occur in the United States in 1978 (Wheeler and Wheeler 1978). Note that this species has actually been in the US since at least the 1950's based on material collected by E.O. Wilson from Mobile, AL (Pers. Comm. Chris Wilson). Brachymyrmex patagonicus, which is the type species, was redescribed by Quiran et al. (2004). A recent publication by MacGown et al (2007) and a poster by MacGown and Hill (2007) presented the known distribution of this species (which appears to be rapidly expanding) in the U.S., figures of all castes, biological and pest status, and brief diagnoses of all castes.
Taxonomic History (provided by Barry Bolton, 2013)
Diagnosis of Female. 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.
Diagnosis of Male. 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 mouth-parts, 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 Figs. 4-6. Full-face views of Brachymyrmex patagonicus: (4) worker, (5) male, and (6) female. Scale bar equals 0.5 mm. 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.
Brachymyrmex patagonicus is most similar to B. obscurior, another exotic species. It differs in the size of the eye, which is much larger in B. patagonicus than in B. obscurior. Additionally, the males of these two species are different in color. Males of B. patagonicus are bicolored with the head and gaster dark brown and the rest of the body (see photo above), including the appendages, being pale yellowish-brown. Males of B. obscurior are concolorous dark brown. Brachymyrmex sp.-01, recorded from Florida, is also dark brown in color, but lacks erect hairs on the body. An undescribed brown species known only from two queens collected from Arkansas (Lloyd Davis, pers. comm.) is unusual in that the queens are tiny, about the size of typical workers. All other known species present in this region are yellowish in color.
Biology and Economic Importance
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 this species is attracted to sweet baits such as honey or cookies (MacGown et al., 2007).
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 alates 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.
US Distribution: This species appears to be very common in northern FL, the southern portions of GA, AL, MS, and most of LA, and has been found in NC, SC, AR, TX, AZ, NV, and CA as well (NV record from Wild, 2008). This exotic species is spreading at an alarming rate and will likely be found in TN before long, if it is not already there.
MacGown, J. A., J.G. Hill, and M. A. Deyrup. 2007. Brachymyrmex patagonicus (Hymenoptera: Formicidae), an emerging pest species in the southeastern United States. Florida Entomologist 90: 457-464. [pdf]
MacGown, J. A. and J. G. Hill. 2007. Brachymyrmex patagonicus (Hymenoptera: Formicidae), an emerging pest species introduced into the southeastern United States. Mississippi Entomological Society 24-26 Oct. 2007. [power point poster]
Mayr, G. 1868. Formicidae novae Americanae collectae a Prof. P. de Strobel. Annuario della Società dei Naturalisti e Matematici, Modena 3: 161-178.
Quiran, E. M., J. J. Martinez, and A. O. Bachmann. 2004. The Neotropical genus Brachymyrmex Mayr, 1868 (Hymenoptera: Formicidae) in Argentina. Redescription of the type species, B. patagonicus Mayr, 1868; B. bruchi Forel, 1912; and B. oculatus santschi, 1919. Acta Zoologica Mexicana 20: 273-285.
Wheeler, G. C. and J. Wheeler. 1978. Brachymyrmex musculus, a new ant in the United States. Entomological News 89: 189-190.
Wild, A. 2008. Myrmecos Blog: Rover Ants (Brachymyrmex patagonicus), an emerging pest species. http://myrmecos.wordpress.com/2008/05/27/rover-ants-brachymyrmex-patagonicus-an-emerging-pest-species/ (accessed 5 June 2008).
Links and Fact Sheets
Layton, B. and J. A. MacGown. 2008. Rover Ants: Mississippi Extension Pest Control Sheet. [pdf]
Myrmecos Blog: Rover Ants (Brachymyrmex patagonicus), an emerging pest species. http://myrmecos.wordpress.com/2008/05/27/rover-ants-brachymyrmex-patagonicus-an-emerging-pest-species/