Brachymyrmex cavernicola

Identification
Wheeler 1938 - At first sight this species might be mistaken for a Nylanderia because of its peculiar erect hairs, or macrochaetae. It is obviously related to Brachymyrmex australis (as Brachymyrmex longicornis) but its worker is stouter, with much smaller eyes, longer median funicular joints, much thicker petiolar node and very different pilosity.

Ortiz-Sepulveda et al. (2019) - The feature that allows distinguishing Brachymyrmex cavernicola from all other Brachymyrmex species is the presence of conspicuous thick black hairs on the head, mesosoma and gaster, which contrast strongly with the yellowish body, a condition reminiscent of Nylanderia. Brachymyrmex antennatus also has erect hairs on the mesosoma that are darker than the tegument; however, these are not as thick as those of B. cavernicola, and in other features these species are very different.

Jack Longino - Face, pronotum, mesonotum, and first gastral tergite covered with coarse black setae; color yellow, strongly contrasting with black setae; eyes very small.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Brazil, Colombia, Costa Rica, Ecuador, Mexico, Peru.

Biology
Jack Longino: This species occurs in low to mid-elevation wet to moist forest habitats, where it appears to be completely subterranean. I have a few records of workers from Winkler and Berlese samples, but I more often collect it by finding nests under stones and in small galleries in clay soil. I do not know what an entire colony is like, but I did find a dealate queen in one nest.

This is a very atypical Brachymyrmex. The coarse black setae sprouting from the pale orange integument makes for a striking appearance. It looks like a cross between Brachymyrmex and some Nylanderia.

This species was previously known only from the types. The types were collected in Mexico, "in the Balaam Canche Cave, Chichen Itza, under a stone near the mouth." (Wheeler 1938). Wheeler included the species in a paper on cavernicolous ant species, but admitted that the line between truly cavernicolous ants and subterranean ants was not sharp (he referred to subterranean ants as "microcavernicolous"). It is clear that this species is not associated with caves in any special way.

Nomenclature

 * . Brachymyrmex cavernicola Wheeler, W.M. 1938: 252 (w.m.) MEXICO (Yucatan).
 * Status as species: Kempf, 1972a: 38; Bolton, 1995b: 82; Branstetter & Sáenz, 2012: 255; Fernández & Ortiz-Sepúlveda, 2019: 728; Ortiz-Sepúlveda, et al. 2019: 479 (redescription).

Worker
Length 1.5-2 mm.

Head nearly square, with feebly and evenly convex sides and straight posterior border. Eyes at the middle of the sides, small, moderately convex, with only about 12 facets in their greatest diameter, less than half as long as the distance between their anterior orbits and the anterior corners of the head. Clypeus large, very convex behind but not carinate, its anterior border subangularly produced. Mandibles narrow, with oblique, 5-toothed apical borders, the teeth large and subequal, except the median one, which is minute. Frontal area distinct, triangular, impressed; frontal carinae short, subparallel. Antennae 9-jointed as in the other species of the genus, long and slender; scapes extending fully one-third their length beyond the posterior border of the head; joints 2-7 of funiculus subequal, twice as long as broad, first joint shorter, terminal joint as long as the two preceding joints together. Thorax with distinct promesonotal, mesometanotal and metaepinotal sutures, distinctly impressed dorsally at the mesometanotal suture, the metaepinotal oblique on each side and confluent with the mesometanotal suture in the middle; metanotal spiracles not prominent. Seen from above the pronotum is broad and semicircularly rounded anteriorly, more than twice as broad as long without the neck; mesonotum semicircular, also slightly more than twice as broad as long; epinotal declivity sloping, flattened. widening posteriorly, fully three times as long as the slightly convex base. Petiole with low, thick, anteriorly inclined node, which, seen from behind, has a rounded and slightly acuminate superior border. Gaster voluminous, of the usual shape. Legs rather slender.

Shining; very finely and superficially reticulate, the head more distinctly than the body.

Erect hairs very coarse and conspicuous, dark brown, arranged in two parallel longitudinal rows on the front and vertex, shorter on the posterior corners of the head. longer, sparser and paler on the c1ypeus; pro- and mesonotum each with a few of these brown hairs but there are none on the epinotum; on the dorsum of the gaster they are numerous and regularly arranged. Appendages with rather abundant. fine. white, appressed or subappressed pubescence; gula with similar but more dilute pubescence.

Yellow; appendages slightly paler; dorsum of gaster and posterior portion of head brownish.

Ortiz-Sepulveda et al. (2019) - Additional material (n = 10). HL1 0.51–0.57; HL2 0.35–0.41; HL3 0.13–0.18; HW 0.45–0.51; SL 0.54–0.63; EL 0.09–0.10; WL 0.51–0.63; PnL 0.19–0.21; PnW 0.29–0.35; ML 0.10–0.13; MW 0.18– 0.22; Indices CI 83.33–91.67; SI1 118.18–134.62; SI2 139.53–166.67; OI1 17.54–20.83; OI1 25.00–31.25.

Head. Slightly longer than wide in full face view; posterior cephalic margin slightly concave. Thick hairs cover the front of the head. Clypeus with a rounded anterior margin and five long, erect hairs of which a single hair is near the anterior margin, two hairs are in mediolateral position, and two more near the toruli; other hairs on the clypeus are markedly 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 of approximately 2.0× the maximal diameter of the eyes and bear appressed or decumbent hairs. Ocelli are absent or one central ocellus is present. Eyes are positioned on the cephalic midline and have 7–8 ommatidia along their maximal diameter.

Mesosoma. With several thick erect hairs on the promesonotum (> 2), and two between the metathoracic spiracles, but none on the propodeum. The mesonotum is not inflated and does not bulge dorsally above the pronotum in lateral view. Metanotal groove wider than the diameter of the metathoracic spiracles. Metathoracic spiracles in dorsolateral position, not protruding, and not touching any suture. Dorsum of the propodeum is weakly convex and shorter than the posterior slope. Propodeal spiracles circular, positioned just ventrally of the posterior propodeal margin slightly posterior of the middle of the propodeal slope. Legs with appressed and scattered suberect hairs. Petiole short and inclined forward.

Gaster. With scarce pubescence but densely covered by thick, erect hairs.

Color and sculpture. Body smooth and shiny, except for the dorsum of the mesosoma which sometimes has slightly imbricate sculpture. The body color is typically yellowish, although the head and gaster are sometimes darker than the mesosoma. Tegument color contrasts with the thick black hairs.

Male
Length about 1.3 mm.

Head, small, flat, as broad as long, narrower in front than behind, with convex sides and straight posterior border. Eyes large but not convex; ocelli widely separated, large but not prominent. Mandibles small, narrow, with truncated, edentate tips. Clypeus small, flattened, its anterior border produced in the middle as a blunt point. Frontal carinae very short; frontal area like that of the worker but not impressed. Antennae 10-jointed; scapes extending beyond the posterior border of the head; first funicular joint slightly swollen, nearly twice as long as broad; joints 2-8 subequal, nearly one and one-half times as long as broad, terminal joint as long as the three preceding joints together. Thorax elliptical, much broader than the head; mesonotum large, as long as broad, very convex and semicircularly projecting over the pronotum, flattened behind; scutellum large and convex; epinotum small, feebly convex and sloping. in profile without distinct base and declivity. Petiolar node small, its superior border straight and transverse, much sharper than in the worker. Gaster-shaped as in this caste; genitalia small, exserted; stipites subtriangular, with rounded tips; volsellae somewhat uncinate. Legs slender.

Shining, like the worker very finely and obscurely reticulate.

Brown erect hairs very short, present only on the mesonotum and scutellum; remainder of body and appendages invested with very fine, appressed, white pubescence. Pale yellow; mesonotum brownish, posterior portion of head dark brown. Wings opaque white, with white veins.

Type Material
Described from 34 workers and a single male taken by Dr. Pearse in the Balaam Canche Cave, Chichen Itza, under a stone near the mouth.

Ortiz-Sepulveda et al. (2019) - Lectotype worker (: USNMENT00529073) and Paralectotype workers, male (USNM: USNMENT00529073; MCZC: M.C.Z. Cotype 17–1922428, M.C.Z. Cotype 11–1322428, M.C.Z. Cotype 23–2522428, M.C.Z. Cotype 14–1622428, M.C.Z. Cotype 1–322428, M.C.Z. Cotype 5–722428, M.C.Z. Cotype 422428; here designated): 21 workers, one male [examined]. MEXICO: Yucatan: Chichenitza, Balaam Canche Cave, H.S. Pearse, 13 June 1936.

References based on Global Ant Biodiversity Informatics

 * Dattilo W. et al. 2019. MEXICO ANTS: incidence and abundance along the Nearctic-Neotropical interface. Ecology https://doi.org/10.1002/ecy.2944
 * Fernandes, P.R. XXXX. Los hormigas del suelo en Mexico: Diversidad, distribucion e importancia (Hymenoptera: Formicidae).
 * Franco W., N. Ladino, J. H. C. Delabie, A. Dejean, J. Orivel, M. Fichaux, S. Groc, M. Leponce, and R. M. Feitosa. 2019. First checklist of the ants (Hymenoptera: Formicidae) of French Guiana. Zootaxa 4674(5): 509-543.
 * Kempf, W.W. 1972. Catalago abreviado das formigas da regiao Neotropical (Hym. Formicidae) Studia Entomologica 15(1-4).
 * Longino J. T. 2013. Ants of Nicargua. Consulted on 18 Jan 2013. https://sites.google.com/site/longinollama/reports/ants-of-nicaragua
 * Longino J. T. L., and M. G. Branstetter. 2018. The truncated bell: an enigmatic but pervasive elevational diversity pattern in Middle American ants. Ecography 41: 1-12.
 * Longino J. et al. ADMAC project. Accessed on March 24th 2017 at https://sites.google.com/site/admacsite/
 * 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
 * Reddell J. R., and J. C. Cokendolpher. 2001. Ants (Hymenoptera: Formicidae) from caves of Belize, Mexico, and California and Texas (U.S.A.) Texas. Texas Memorial Museum Speleological Monographs 5: 129-154.
 * Smith M. A., W. Hallwachs, D. H. Janzen. 2014. Diversity and phylogenetic community structure of ants along a Costa Rican elevational gradient. Ecography 37(8): 720-731.
 * Vásquez-Bolaños M. 2011. Lista de especies de hormigas (Hymenoptera: Formicidae) para México. Dugesiana 18: 95-133
 * Wilson C. M., A. Smith-Herron, and J. L. Cook. 2016. Morphology of the male genitalia of Brachymyrmex and their implications in the Formicinae phylogeny. Journal of Hymenoptera Research 50: 81-95.