Brachymyrmex obscurior

A common species with an ostensibly large range. It is possible that this name, as applied across the current range of Brachymyrmex obscurior, is comprised of a number of closely allied species.

Identification
Ortiz-Sepulveda et al. (2019) - Brachymyrmex obscurior morphologically resembles Brachymyrmex cordemoyi and Brachymyrmex patagonicus because all three species have a metanotal groove that is absent or narrower than the diameter of metathoracic spiracles, their mesonotum does not bulge dorsally above the pronotum, their scapes usually surpass the posterior margin of the head, and their bodies are brownish. Brachymyrmex obscurior and B. cordemoyi differ from B. patagonicus, however, because they have dense pubescence on the gaster. Brachymyrmex obscurior differs from B. cordemoyi by having less conspicuous dense pubescence on the dorsum of the head and the mesosoma, dense decumbent pubescence on the gaster, and eyes with fewer ommatidia along their maximal diameter (on average 9 instead of 10–12).

Distribution
This Central American and Caribbean species has spread to Canada and the United States through human activity (Deyrup, Davis & Cover, 2000).

Distribution based on Regional Taxon Lists
Australasian Region: New Caledonia. Indo-Australian Region: Guam, Hawaii, Marshall Islands, Northern Mariana Islands, Samoa. Nearctic Region: United States. Neotropical Region: Argentina, Barbados, Brazil, British Virgin Islands, Chile, Colombia, Dominican Republic, Greater Antilles, Grenada, Guatemala, Haiti, Lesser Antilles, Martinique, Mexico, Netherlands Antilles, Puerto Rico.

Biology
Brachymyrmex are general scavengers, with numerous species known to tend root aphids and coccids. The description of this species was provided in a paper by Forel (1893) that treated ants collected by H. H. Smith on the island of St. Vincent. Smith was appointed by the British government to study the fauna and flora of the West Indies. Forel included the collection notes provided by Smith for each species given in the paper (see next section). These notes are interesting from a historical perspective and also for the natural history information they provide.

In Florida this species occurs on beaches as well as in all kinds of open, artificially disturbed sites. Smith (1933) considered that it was probably introduced. One of the authors once saw queens land inside a small airplane with an open door in Fort Lauderdale, and head for the open door again when the plane landed in San Salvador in the eastern Bahamas. It often occurs in potted plants. There is a very good chance that this species was transported to Florida in commerce early and often, but it could also have been already naturally established, having moved around the Gulf of Mexico. The taxonomy and consequently the distribution of the brown Brachymyrmex is very uncertain. As in the cases of most other dubiously native neotropical species in Florida, the only chance to show that this species was imported would be a genetic study that showed that the Florida population is most closely related to populations that are unlikely to have reached Florida without assistance. Showing that the species was native would be just as problematic, requiring evidence of genetic distinctness of the Florida population, or pre-Columbian specimens. (Deyrup, Davis & Cover, 2000.)

Regional Notes - St Vincent
The opening text of the source paper (Forel 1893) for the following Brachymyrmex obscurior collection records, by H. H. Smith, states "These notes are given in full, as it is thought that the precise localities in which the species were met with may be of interest to local naturalists."

(57). Moderately common in communities of a few hundreds at most. The formicarium is formed under a stone, or at the roots of grass and weeds, generally on open ground ; but if my hasty identifications are correct, the species ranges to the tops of the highest mountains. So far as 1 have observed, the formicarium consists only of one or two simple chambers, with a short connecting passage. The ants are moderately active, less so than allied forms. They are sometimes beaten from foliage.

(57 a). Wallibou (leeward) ; thickets near the seashore. Oct. 6th. Community of several hundreds under a stone. Sandy ground.

(57 b). Cumberland (leeward); open valley near the sea-level. Male and female found together under a stone (not copulated). Oct. 8th.

(57 c). Islet fronting Chateaubelais Bay (leeward), Oct. 31st. Rocky ground, thickets near sea-level. Workers found scattered under stones.

(57 d). Workers. Note was lost. Probably obtained by beating.

(57 e). Soufriere Volcano, 2500 ft. Sept. Scrubby growth found in moss.

(57f). Wallilobo Valley (leeward), Nov. 8th; open hill-side, 500 ft. A female referred to this species, found alone under sod on a rock.

(57 g). Bowwood Valley, near Kingstown, 800 ft. Oct. 15th. Second growth, beaten from branches.

(57 h). Not noted. Doubtfully referred to this species.

(57 i). Windward side; open sandy valley of the Dry River, near the sea. Jan. 2nd. From two nests under stones. The species is common in this vicinity.

(57 j). Same locality and date as (57 i). An unusually large community under a stone. The winged females and males (especially the males) were very numerous.

(57 k). Bank near seashore, between Georgetown and the Dry River (windward). Jan. 3rd. Nest at the roots of grass.

(57 l). Workers, doubtfully referred to this species; near Grand Sable Estate (windward). Jan 3rd. Seashore thicket; side of a rock under loose earth.

Nomenclature

 * . Brachymyrmex heeri var. obscurior Forel, 1893g: 345 (w.q.m.) ST VINCENT & THE GRENADINES (St Vincent I.).
 * Subspecies of heeri: Forel, 1897b: 298; Forel, 1899c: 123; Wheeler, W.M. 1905b: 111, 132; Forel, 1905b: 160; Wheeler, W.M. 1906e: 350; Wheeler, W.M. 1908a: 153; Wheeler, W.M. 1911a: 29; Forel, 1912i: 62; Wheeler, W.M. 1917g: 462; Mann, 1920: 431; Wheeler, W.M. 1923c: 5; Santschi, 1923b: 666; Emery, 1925b: 42; Stärcke, 1926: 118 (in key); Menozzi, 1929a: 3; Menozzi & Russo, 1930: 166; Smith, M.R. 1937: 866; Wheeler, W.M. 1942: 253; Smith, M.R. 1951a: 839; Smith, M.R. 1954c: 11; Kempf, 1972a: 39; Alayo, 1974: 43; Deyrup, 2017: 181.
 * Status as species: Brown, 1957e: 237; Smith, M.R. 1967: 366; Wilson & Taylor, 1967: 92; Taylor, 1976a: 88; Smith, D.R. 1979: 1424; Deyrup, et al. 1989: 99; Brandão, 1991: 331; Dlussky, 1994: 55; Bolton, 1995b: 82; Deyrup, 2003: 44; Wetterer & Vargo, 2003: 417; Wetterer & Wetterer, 2004: 215; Clouse, 2007b: 210; Branstetter & Sáenz, 2012: 255; Sarnat, et al. 2013: 69; Fernández & Ortiz-Sepúlveda, 2019: 729; Lubertazzi, 2019: 78; Ortiz-Sepúlveda, et al. 2019: 518 (redescription).

Ortiz-Sepulveda et al. (2019) - Forel (1893) described B. obscurior as a variety of Brachymyrmex heeri and indicated that it differs from typical B. heeri by having a brownish instead of yellowish body and slightly denser pubescence on the gaster. We observed that both species can readily be distinguished as to whether or not the mesonotum bulges dorsally above the pronotum in lateral view. Forel (1893) also reported that B. obscurior resembles B. patagonicus but that both taxa differ as to the presence or absence of ocelli, in body size, as to pubescence and the length of the scapes. He further considered B. obscurior to be a difficult “form” that represents a morphological transition between B. patagonicus and B. heeri (Forel 1912a). We agree that B. obscurior and B. patagonicus are morphologically very similar, and molecular studies of both taxa will be required to examine whether they are distinct species. Wilson and Taylor (1967) recognized B. heeri var. obscurior as a distinct species as a provisional measure in anticipation of a full-scale revision of the genus. We agree with this decision, based on the morphological differences indicated above, but we cannot for now comment on their proposed synonymization of B. heeri var. aphidicola Wheeler, 1934 to B. obscurior, as this material from Hawaii was not available to us.

Description
Cette differe de la forme typique que par sa couleur brunutre et par ses ailes legerement enfumees de brunatre. La pubescence est peut etre aussi legerement plus forte. (This form differs from the typical one only by its brownish color and by its slightly brownish smoked wings. The pubescence is perhaps also slightly stronger.)

Cette forme se distingue du Brachymyrmex patagonicus Mayr, par l'absence des ocelles, par sa taille plus petite et par sa pilosite un peu plus abondante. Les scapes sont aussi un peu plus longs. (This form differs from Mayr's Brachymyrmex patagonicus by the absence of ocelli, by its smaller size and by its slightly more abundant pilosity. The scapes are also a little longer.)

Worker
Ortiz-Sepulveda et al. (2019) - Lectotype and paralectotypes (n = 8). HL1 0.39–0.47; HL2 0.27–0.35; HL3 0.10–0.12; HW 0.35–0.48; SL 0.35–0.45; EL 0.10–0.15; WL 0.31–0.53; PnL 0.09–0.15; PnW 0.23–0.30; ML 0.06–0.14; MW 0.15–0.23; Indices CI 79.17–106.67; SI1 96.59–115.79; SI2 125.71– 1146.67; OI1 25.00–31.25. Additional material (n = 2). HL1 0.44–0.47; HL2 0.30–0.32; HL3 0.11–0.12; HW 0.37– 0.42; SL 0.38–0.41; EL 0.11–0.12; WL 0.42–0.47; PnL 0.11–0.13; PnW 0.26–0.30; ML 0.11; MW 0.18–0.19; Indices CI 84.34–88.89; SI1 96.25–102.86; SI2 126.32–128.33; OI1 28.57–28.75; OI2 24.10–24.44.

Head. Slightly longer than wide in full face view; posterior cephalic margin slightly concave. Dorsum of the head with sparse appressed hairs. Clypeus with a rounded anterior margin and five long, erect hairs of which a single, usually conspicuous hair is near the anterior margin, two hairs are in mediolateral position, and two more near the toruli; other hairs on the clypeus are clearly shorter and appressed or decumbent. Toruli surpassing the posterior clypeal margin in oblique anterodorsal view. The scapes surpass the posterior cephalic margin by a length up to the maximal diameter of the eye, and they have appressed hairs. Ocelli absent. Eyes are positioned on the cephalic midline and have 8–10 ommatidia along their maximal diameter.

Mesosoma. Typically with two erect hairs on the pronotum and two on the mesonotum. The mesonotum is not inflated and does not bulge dorsally above the pronotum in lateral view. Metanotal groove absent or narrower than the diameter of the metathoracic spiracles. Metathoracic spiracles in dorsolateral position, not protruding, and typically touching the mesometanotal and propodeal sutures. Dorsum of the propodeum convex and shorter than the propodeal slope. Propodeal spiracles circular and positioned on the posterior propodeal margin, slightly anterior of the middle of the propodeal slope. Legs with appressed hairs. Petiole short and inclined forward.

Gaster. With decumbent dense pubescence and several scattered long erect hairs.

Color and sculpture. Body smooth and shiny, except for the dorsum of the mesosoma which is sometimes slightly imbricate. Body uniformely brownish, but with slightly lighter antenna and legs.

Type Material
Ortiz-Sepulveda et al. (2019) - Lectotype worker (: USNMENT00757132) and paralectotype workers, queens, males (MHNG: USNMENT00757132–00757135; USNMENT00758124– 00758128; here designated): 16 workers, three queens, three males [examined]. ANTILLES: Saint Vincent.

The specimen at the top of pin MHNG: USNMENT00757132 is designated here as the lectotype, whereas the other ants are paralectotypes.

References based on Global Ant Biodiversity Informatics

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