Myrmelachista mexicana

The types were collected from hollow twigs. Gillette et al. (2015) in a Chaipas, Mexico field study of twig-nesting ants in coffee plants found M. mexicana nesting on plants between 1150-1300 m in elevation.

Identification
Longino (2006) - Worker with antenna 10-segmented, face shiny, HW less than 0.5mm.

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

Biology
Longino (2006) - The types of M. mexicana were collected in hollow twigs in southern Mexico. A dealate queen at USNM was intercepted by Brownsville quarantine in an orchid stem from the Canal Zone in Panama. At La Selva Biological Station and on the Barva transect in Braulio Carrillo National Park it has been collected in several Project ALAS Malaise and canopy fogging samples, from 50 to 500m elevation.

At La Selva I found a colony in a small dead stem in the crown of a recently felled Carapa guianensis. The relict tree was somewhat isolated in low second growth vegetation, and there were abundant vines over the crown, mainly Marcgraviaceae. The colony was polygynous, with multiple dealate queens. In the field, the tiny workers looked like small Solenopsis or Monomorium floricola.

Nomenclature

 *  mexicana. Myrmelachista (Decamera) mexicana Wheeler, W.M. 1934g: 200, fig. 4 (w.q.m.) MEXICO. Combination in M. (Hincksidris): Kempf, 1972a: 149. See also Longino, 2006a: 39.

Worker
Length 1.5-2 mm.

Head small, convex above and behind, rounded subrectangular, distinctly longer than broad, scarcely broader behind than in front, with rather convex sides and straight posterior borders. Eyes flat, at the middle of the sides. Clypeus moderately convex, almost subcarinate, its rounded anterior border with a small, acute median tooth. Frontal carina: short, straight, parallel, nearly as far apart as their distance from the lateral borders of the head. Mandibles convex, 5-toothed. Scapes of the 10-jointed antenna: reaching half way between the posterior orbits and the rounded posterior corners of the head; first funicular joint fully twice as long as broad; joints 2-6 small, the second as long as broad, 3-6 slightly broader than long; club large, its two basal joints subequal, longer than broad, together nearly as long as the decidedly more swollen terminal joint. Thorax slender, narrower than the head, hour-glass shaped, with the mesoepinotal constriction deep both dorsally and laterally; promesonotum oval, broader •and somewhat larger than the epinotum; mesonotum as long as broad, broader in front than behind; metaepinotal suture distinct, metanotal spiracles large and prominent, epinotum in profile evenly rounded, without differentiated base and declivity, somewhat lower than the promesonotum, the posterior portion of the declivity slightly concave. Petiole small, narrow, much longer than high, with long posterior peduncle; scale thick, strongly inclined forward, the very blunt summit of the scale strongly rounded and entire when seen from behind. Gaster small, elliptical, with pointed tip. Legs slender, only the fore femora slightly enlarged.

Smooth and shining, with small, sparse, piligerous punctures; mandibles punctate-striate; clypeus obscurely striate; upper surface of epinotum reticulate.

Pilosity glistening white, sparse, bristly, erect or suberect on the body; shorter and more abundant on the appendages, erect on the scapes, conspicuous on the funiculi, more oblique on the legs.

Deep castaneous; mandibles and clypeus reddish; pronotum, trochanters and tarsi paler, more yellowish brown.

Longino (2006) - HL 0.438–0.471, HW 0.389–0.423, SL 0.256–0.292, EL 0.093–0.100, CI 87–90 (n=5).

Antenna 10-segmented; maxillary palpus 6-segmented; mandible, clypeus, and face smooth and shining; in full face view, sides of head with sparse, short, appressed pubescence, no erect setae; rear margin of head with longer erect setae; ventral surface of head with very sparse, very short appressed pubescence, no erect setae; hind tibia with abundant appressed to suberect setae, pilosity short, about 1/4 width of tibia; mesosoma strongly constricted at metanotal groove, hourglass-shaped; dorsal face of propodeum with faint to pronounced reticulate sculpture; petiole in side view with low, rounded node, short anterior peduncle and long posterior peduncle; bicolored, with light red brown head and mesosoma, dark brown gaster, or grading to more uniformly dark red brown coloration.

Queen
(dealated). Length nearly 4 mm.

Long and slender. Head strongly rectangular, one and one-third times as long as broad, convex above, slightly broader behind than in front, with straight sides and posterior border. Eyes rather large, nearly flat, in front of the middle of the sides; ocelli small, widely separated. Mandibles very convex, with stout teeth. Clypeus convex, with a stout, blunt upturned tooth at the middle of its anterior border. Thorax from above elliptical, nearly two and one-half times as long as broad, somewhat broader than the head; mesonotum flat, subcircular, as long as broad; epinotum small, sloping, scarcely convex in profile, without distinct base and declivity. Petiole as in the worker, but the node with more broadly rounded superior border. Gaster large, elongate elliptical.

Sculpture, pilosity and color as in the worker, except that the mandibles are red and the thorax is deep castaneous throughout.

Longino (2006) - HL 0.570–0.599, HW 0.483–0.484, SL 0.285–0.297, EL 0.175–0.180, OW 0.032, OD 0.147–0.156, CI 81–85, OI 36–37, OcI 5–6 (n=2).

Similar to worker in meristic characters, patterns of sculpture, pilosity, coloration. Labrum short, bilobed.

Male
Length 1.5-2 mm.

Head through the eyes distinctly broader than long, convex and subcircular behind, cheeks short, straight and converging anteriorly. Mandibles narrow, edentate, pointed at their tips and strongly geniculate at their bases. Eyes large; ocelli very small and widely separated. Clypeus short, its anterior border with a very minute median denticle. Antennre ll-jointed, slender; scapes about eight times as long as broad; first funicular joint somewhat swollen, pyriform, nearly twice as long as broad; second joint as long as broad; joints 3-6 slightly broader than long; 8-9 as broad as long, together as long as the last joint of the rather indistinct 4-jointed club. Thorax long, broader than the head; pronotum small; mesonotum elliptical, longer than broad, flattened posteriorly, very convex anteriorly; epinotum small and sloping as in the female; mesosterna long but flattened. Petiole short, without posterior peduncle; scale low, thick, nodiform, with rounded summit. Gaster elliptical; genitalia small but exserted. Legs slender. Fore wings broad, with well developed pterostigma and closed marginal cell; cubital and discoidal veins imperfect, discoidal cell absent.

Sculpture and pilosity much as in the worker; head, thorax and petiole somewhat paler, more piceous or reddish brown; gaster darker; mandibles, antennae, legs and genitalia brownish or sordid yellow. Wings colorless, with pale yellow veins and pterostigma.

Longino (2006) - Wheeler’s figure of male genitalia show similarities to Myrmelachista zeledoni, with blunt basiparamere lobe and paramere, and strongly upturned penial valve (suggesting that apodeme meets dorsal margin at right angle, like zeledoni). The volsella is not visible in the illustration, suggesting it is short and downturned, like zeledoni. Pygostyles are not shown, suggesting they are absent or minute.

Type Material
Described from four workers, one female and seven males (No. 296), taken by Dr. Skwarra at Mirador, Vera Cruz in hollow twigs.

Longino (2006) - Syntype workers, queen, males: Mexico, Veracruz, Mirador (Skwarra #296), in hollow twigs,  (USNM syntype worker examined).

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
 * Kempf, W.W. 1972. Catalago abreviado das formigas da regiao Neotropical (Hym. Formicidae) Studia Entomologica 15(1-4).
 * Larsen, A., and S. M. Philpott. 2010. Twig-nesting ants: the hidden predators of the coffee berry borer in Chiapas, Mexico. Biotropica 42: 342-347.
 * Longino J. T. 2006. A taxonomic review of the genus Myrmelachista (hymenoptera: Formicidae) in Costa Rica. Zootaxa 1141: 1-54
 * Longino J. et al. ADMAC project. Accessed on March 24th 2017 at https://sites.google.com/site/admacsite/
 * Rojas Fernandez P. 2010. Capítulo 24. Hormigas (Insecta: Hymenoptera: Formicidae). In: Diversidad Biológica de Veracruz. Volumen Invertebrados. CONABIO-Gobierno del Estado de Veracruz.
 * Vasquez-Bolanos M. 2011. Checklist of the ants (Hymenoptera: Formicidae) from Mexico. Dugesiana 18(1): 95-133.
 * Vásquez-Bolaños M. 2011. Lista de especies de hormigas (Hymenoptera: Formicidae) para México. Dugesiana 18: 95-133
 * Wheeler W. M. 1934. Neotropical ants collected by Dr. Elisabeth Skwarra and others. Bulletin of the Museum of Comparative Zoology 77: 157-240.