Brachymyrmex nebulosus

In Costa Rica this species has been collected only three times, from two nearby sites on the Pacific slope just below Monteverde Cloud Forest Reserve in Costa Rica. Both sites are about 800 m elevation and are in the moist forest transition zone between cloud forest and lowland dry forest climate zones. Both areas were mosaics of forest patches, pastures, scrubby vegetation, and road edges. All three collections have been of workers on vegetation in open scrubby vegetation. In the field, these ants look and behave remarkably like Crematogaster. (LaPolla and Longino 2006)

Identification
LaPolla and Longino (2006) - Face smooth, with abundant erect setae; scapes surpass posterior margin of head by about length of first funicular segment; metanotum deeply impressed, mesosoma hour-glass shaped; erect hairs on legs.

The size and shape of the mesosoma is very similar to Myrmelachista zeledoni, a common species found sympatrically with Brachymyrmex nebulosus. The visual similarity in the field to Crematogaster is shared by Brachymyrmex nebulosus with several montane Myrmelachista species.

This species is easy to distinguish from other Brachymyrmex species in Costa Rica. A distinctly large Brachymyrmex, B. nebulosus possesses the following diagnostic traits: blackish-brown and shiny, hour-glassed shaped mesonoma, and legs and scapes with erect hairs. The hour-glass shaped mesonoma could only be confused with Brachymyrmex santschii which possesses a similarly shaped mesonoma, but it is not as well-defined as in B. nebulosus and the ant overall is smaller, much lighter in color (brownish yellow), and the cuticle is not shiny. Finally, B. santschii does not have erect hairs on the legs or scapes. Erect hairs on the legs and scapes are what Santschi (1923) used to define the subgenus Bryscha Santschi. The monophyly of Bryscha has been questioned (Brown 1973) and Bolton (2003) recently synonymized the subgenus under Brachymyrmex. While a phylogeny of Brachymyrmex is not within the scope of this study, it is worth noting that erect hairs on the legs and scapes are rarely observed in Brachymyrmex and may be of phylogenetic importance. Only four other species have been reported with erect hairs on the legs and scapes (this has only been confirmed by us for Brachymyrmex gaucho): Brachymyrmex antennatus, B. gaucho, Brachymyrmex micromegas and Brachymyrmex pilipes.

Based on worker morphology, the closest relative to B. nebulosus appears to be B. gaucho, which is known only from its type locality in Argentina. Like B. nebulosus, B. gaucho is a large, black, and shiny species. Unfortunately, the holotype of B. gaucho (and the only known specimen) has been badly damaged, with only the broken head and gaster remaining (holotype worker examined [JSL], ARGENTINA: Cordoba: Unguillo, in NHMB). Nonetheless, comparison of the holotype with B. nebulosus was possible. The main morphological difference between the two species appears to be that the erect hairs on B. gaucho are much shorter than those observed on B. nebulosus, especially on the gaster.

Ortiz-Sepulveda et al. (2019) - Brachymyrmex nebulosus differs from other Brachymyrmex species in having a clypeus with its medial portion forming a conspicuous “lip,” its hour-glass shaped mesosoma and it has portions of the head and mesosoma that bear alveolate sculpture. Brachymyrmex musculus is the only other Brachymyrmex species known to date that has a clypeus with a somewhat developed medial lip, but it is less conspicuous than in B. nebulosus.

Distribution based on Regional Taxon Lists
Neotropical Region: Costa Rica, Honduras, Mexico.

Nomenclature

 * . Brachymyrmex nebulosus LaPolla & Longino, 2006: 299, fig. 1 (w.) COSTA RICA.
 * Status as species: Ortiz-Sepúlveda, et al. 2019: 517.

Ortiz-Sepulveda et al. (2019) - Brachymyrmex nebulosus has been originally described from Costa Rica, but during our studies we came across two specimens from Mexico that very strongly resemble this species. The only differences are that the Mexican specimens have a more squared head, and stronger alveolate sculpture on the head and the dorsum of the mesosoma. Considering these differences and the geographical distribution, these Mexican specimens may be a variety of B. nebulosus, or potentially a different species, although more material and further study would be required to resolve this issue.

Worker
Holotype worker: TL: 2.90 mm; HL: 0.767 mm; HW: 0.704 mm; SL: 0.736 mm; ML:0.892 mm; GL: 1.24 mm; CI: 92; SI: 105.

Head dark brown, with scapes and mandibles lighter brown to dusty yellow; smooth and shiny; abundant suberect to erect hairs throughout, with longest along posterior margin and clypeus; posterior margin entire; antenna 9-segmented; scape with abundant, short suberect to erect hairs; scapes surpass posterior margin by length of first funicular segrnent; 3 small ocelli present, though lateral ocelli often difficult to distinguish; clypeus broad with xnedian portion extended from margin forming a “lip”; mandible with 5 teeth, apical and 4th (measured from apical) longest. Mesosoma dark brown; roughly hour-glass shaped; smooth and shiny, with erect hairs on pronotal dorsum; katepisternum and side of propodeum shagreened; declivity short and indistinct; legs dark brown with abundant suberect to erect hairs; tarsi lighter in color. Petiole short and inclined forward. Gaster dark brown, with appressed to erect hairs throughout.

Ortiz-Sepulveda et al. (2019) - Paratype. HL1 0.67; HL2 0.40; HL3 0.24; HW 0.63; SL 0.62; EL 0.18; WL 0.80; PnL 0.29; PnW 0.45; ML 0.26; MW 0.23; Indices CI 94.67; SI1 97.18; SI2 153.33; OI1 28.17; OI2 36.00. Additional material (n = 1). HL1 0.80; HL2 0.49; HL3 0.23; HW 0.73; SL 0.72; EL 0.20; WL 0.92; PnL 0.31; PnW 0.50; ML 0.12; MW 0.27; Indices CI 91.11; SI1 98.78; SI2 111.76; OI1 15.79; OI2 n.a.

Type Material
Holotype worker, COSTA RICA: Puntarenas Prov.; 6 km south of Monteverde; l0°15'N, 84°49'W; 800 m; 22 June 1990 (J. Longino #4050) ( ENT 143546) ; 1 paratype worker data same as holotype (INBC); 2 paratype workers COSTA RICA: Puntarenas Prov.; Ojo de Agua; 10°16'N, 84°50'W; 800 m; 5 July 1991 (J. Longino #2965) (INBIOCRI001279916) ; 2 paratype workers COSTA RICA: Puntarenas Prov.; Ojo de Agua; l0°16'N, 84°50'W; 800 m; 28 July 1984 (INBIOCRI002281199)  (LACM).

Etymology
The specific epithet, nebulosus, is Latin for misty or cloudy in reference to the type locality being near Monteverde Cloud Forest Reserve and to the fact the generic designation of this species was in doubt for a time.

References based on Global Ant Biodiversity Informatics

 * Branstetter M. G. and L. Sáenz. 2012. Las hormigas (Hymenoptera: Formicidae) de Guatemala. Pp. 221-268 in: Cano E. B. and J. C. Schuster. (eds.) 2012. Biodiversidad de Guatemala. Volumen 2. Guatemala: Universidad del Valle de Guatemala, iv + 328 pp
 * Longino, J.T. 2010. Personal Communication. Longino Collection Database
 * Ortiz-Sepuvelda C. M., B. Van Bocxlaer, A. D. Meneses, and F. Fernandez. 2019. Molecular and morphological recognition of species boundaries in the neglected ant genus Brachymyrmex (Hymenoptera: Formicidae): toward a taxonomic revision. Organisms Diversity & Evolution https://doi.org/10.1007/s13127-019-00406-2