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
Small workers (1-2mm) with nine segmented antenna. Erect hairs on gaster, no erect hairs on head or mesosoma.

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
Indo-Australian Region: Guam, Hawaii, Marshall Islands, Northern Mariana Islands, Samoa, Solomon Islands, Vanuatu. Nearctic Region: Canada, United States. Neotropical Region: Bahamas, Barbados, Bermuda, British Virgin Islands, Colombia, Costa Rica, Cuba, Dominican Republic, Greater Antilles, Grenada, Guatemala, Haiti, Lesser Antilles, Mexico, Panama, Puerto Rico, Trinidad and Tobago, Venezuela.



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

 *  obscurior. Brachymyrmex heeri var. obscurior Forel, 1893g: 345 (w.q.m.) ANTILLES. Subspecies of heeri: Forel, 1897b: 298; Forel, 1912i: 62. Raised to species: Wilson & Taylor, 1967: 92.

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.

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.