Brachymyrmex patagonicus

Distinguished from other Brachymyrmex species by the combination of: nine-segmented antennae (shared with all congeners), long hairs on the mesosoma, relatively large eyes, and sparse appressed hairs on the dorsal gaster surface. Previously confused with B. musculus and B. obscurior, which are now synonymized. In the field, small size and dark coloration separate it from larger formicine ants; the lack of a sting and non-aggressive behavior distinguish it from Solenopsis fire ants with which it co-occurs.

In its native range, occupies naturally disturbed habitats. In the introduced range, primarily associated with human-modified environments: buildings (indoor pest), landscaped areas with mulch, bases of trees, leaf litter, wood piles, and trash accumulations. Laboratory studies indicate preference for moist environments. Outdoor populations established in subtropical and temperate regions; indoor occurrences reported in colder climates where outdoor survival is uncertain.

Native: South America (Argentina, Paraguay, and broader distribution including Mexico and Central America). Introduced range: United States (15 states from North Carolina to California, first detected Louisiana 1976), Bahamas, continental Asia, Spain, Martinique. Indoor occurrences: England, Netherlands, Japan. Rapid spread documented: from 7 states in 2007 to 15 states in less than a decade.

Has been observed visiting extrafloral nectaries for nectar. Honeydew from hemipterans is hypothesized to constitute a major dietary component. In laboratory settings, survives on artificial diet containing 30% honey solution, liquid tuna mixture, and caterpillar pieces. Preys on small soft-bodied insects including aphids; photographic documentation shows workers subduing crapemyrtle aphids (Sarucallis kahawaluokalani).

Colonies produce alates (winged reproductive queens and males) that disperse through nuptial flights rather than colony budding. New colonies founded independently by single queens. No specific seasonal data on nuptial flight timing available in sources.

Multicolonial structure: each colony occupies a single nest with maintained aggression toward non-nestmates, contrasting with supercolonial invasive ants. Nestmate recognition mediated by chemical differentiation between colonies; aggression levels correlate with genetic divergence. Aggressive behaviors include biting and formic acid spraying, escalating to fighting. Workers display mutual tolerance between some nests in close proximity (few centimeters). Foraging trails established on exterior walls and surfaces up to 3–4 m from structures. Does not bite or sting humans.

Invasive pest species achieving high population densities in urban environments through multicolonial expansion rather than supercolonial resource monopolization. Coexists with native and introduced ant species including Solenopsis invicta and S. xyloni, species typically intolerant of competitors. Hypothesized role in regulating populations of invasive cactus moth (Cactoblastis cactorum), currently under investigation. Functions as predator of small soft-bodied insects and consumer of liquid carbohydrates in urban food webs.

Significant nuisance pest infesting man-made structures, particularly in the southern United States. Attracted to moisture and food sources in kitchens and bathrooms. Does not bite, sting, or mechanically transmit disease, resulting in lower priority for management compared to more harmful invasive ants. Rapid spread and establishment in new regions facilitated by human commerce and movement of goods.

• Brachymyrmex obscuriorFormerly considered a separate species but synonymized with B. patagonicus based on morphological comparison of specimens from the Louisiana State University Arthropod Collection; historically misidentified as distinct.
• Brachymyrmex musculusFormerly considered a separate species but synonymized with B. patagonicus; part of the same taxonomic confusion resolved through specimen comparison.
• Solenopsis invicta (Red Imported Fire Ant)Co-occurs in the invasive range and similarly small, but distinguished by presence of sting, aggressive behavior, and two-segmented petiole node; B. patagonicus lacks sting and has one-segmented petiole.

Long misidentified as multiple species (B. patagonicus, B. musculus, B. obscurior) due to insufficient morphological study; resolved through systematic comparison of museum specimens. The species' success as an invasive despite lacking the supercolonial structure typical of other invasive ants challenges assumptions about necessary traits for invasion success.

• invasive species
• urban pest
• formicine ant
• multicolonial
• nuisance pest

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Crapemyrtle Aphid: A Cosmopolitan Pest of a Popular Ornamental Tree
• crapemyrtle aphid natural enemies - Entomology Today
• During Quarantine, an Entomologist Takes a Closer Look at a New Invasive Ant Species
• The underdog invader: Breeding system and colony genetic structure of the dark rover ant (Brachymyrmex patagonicus Mayr)
• Divide and conquer: Multicolonial structure, nestmate recognition, and antagonistic behaviors in dense populations of the invasive ant Brachymyrmex patagonicus