Megalomyrmex wallacei

Boudinot et al. (2013) - In August 2005, colonies of M. wallacei were collected at La Selva Biological Station by baiting foraging workers with Keebler Pecan Sandies (n=11). In one observation, a few individuals were capable of clearing a bait station monopolized by hundreds of Pheidole workers in a matter of minutes by dispensing their volatile alkaloid-based venom via erratic behaviors such as bucking, gaster flagging, and side-swipe stinging, where the gaster comes from the side rather than tucked under the ant. Colony size ranged from ~50 to 366 females, 0 to 21 males and ~100 to 250 brood. The number of females includes workers and ~3 to 6 ergatoid queens (fig. 247). Most colonies nested in the leaf litter in twigs, between leaves, within old palm leaf petioles, or between the bark and heartwood of a log. On occasion, a colony would nest in the leaves caught at the base of a short palm 10 to 20 cm above ground. Workers quickly flee with brood and move nesting sites following perturbation. Colonies were collected by C. R. F. Brandão with single alate queens near Manaus, Brazil with similar nesting habits (Brandão 2003).

Identification
Boudinot et al. (2013) - Worker uniquely identified among Central American Megalomyrmex by the following combination: (1) mandible with 5 robust, evenly-spaced, subequal triangular teeth; (2) postpetiolar tergum robustly globose, anterior and posterior and anterior faces with about same curvature; (3) postpetiolar sternum strongly and smoothly bulging, without a denticle. Queen Similarly identifiable as worker, but with larger gaster, ergatoid. Male Recognizable by the minimum presence of the following characters: (1) third antennomere apically flattened and bent; (2) petiolar and postpetiolar nodes strongly globose; (3) postpetiolar sternum strongly and smoothly bulging. Additionally, the blackened piligerous punctae are unique among Central American Megalomyrmex.

The ergatoid queen of Megalomyrmex wallacei may be successfully identified using the worker key. The male is unique among Central American leoninus- and modestus-group males as follows: (1) posterior face of propodeum completely covered in evenly arcing concentric carinae; (2) ventrolateral carina of petiole absent; (3) postpetiolar tergum strongly and evenly convex; (4) postpetiolar sternum strongly and angularly bulging; (5) piligerous punctures on body blackened.

Unreported characters we observed in the Costa Rican and Panamanian material of M. wallacei are: presence of very long ocular setae (longest of any Central American species); postpetiole bulging laterally such that the spiracles are directed ventrally (unique among Central American species of the leoninus- and modestus-groups) lancets of sting apparatus subequal in length to sting shaft, narrow to apex; sting shaft narrow to pointed apex. Future taxonomic work on Megalomyrmex should directly compare South American to Central American material. In addition to differences in sculpturation, and possibly in the shape of the pronotum, Central American specimens are generally larger in all metrics than the South American specimens from Brandão (1990). The elevational range (see distribution section below) supplemented by data from Longino (2010).

Distribution
Costa Rica, Panama, Colombia, Guyana, Brazil (Amazonas, Pará, Rondônia, Tocantins). sea-level to 100 m elevation

Distribution based on Regional Taxon Lists
Neotropical Region: Brazil, Colombia, Costa Rica, Guyana, Panama.

Biology
Longino (2010) - This species occurs in mature wet forest, usually low-elevation rainforest. Brandão (2003) reports the species nesting under leaves on the forest floor, in colonies of up to 300 workers. In Costa Rica, workers have been collected at baits on the forest floor, and one nest was observed at La Selva Biological Station. It was inside a 6cm long rotten cacao pod on the trunk of a cacao tree. The nest contained 93 workers. There was no morphologically distinct queen, but there was abundant brood of all sizes, from eggs to pupae. The workers showed considerable size variation, and larger workers had an enlarged mesonotum.

Castes
M. wallacei has winged queens in Brazil (Brandao 2003) but queens are ergatoid in Costa Rica (Peeters & Adams 2016).

Ergatoid queens have eight ovarioles. Several queens were inseminated in each colony, but only some had active ovaries with yolky oocytes (Peeters & Adams 2016).

Nomenclature

 *  wallacei. Megalomyrmex wallacei Mann, 1916: 445, pl. 3, fig. 28 (w.q.) BRAZIL. Brandão, 2003: 150 (m.). See also: Brandão, 1990: 426.

Worker
Brandão (1990) - Mandibles striate; clypeal border not denticulate; frontal suture not impressed; occipital margin raised and visible (frontal view); compound eyes interrupting lateral margins of head capsule in frontal view; dorsal profile of pronotum round; promesonotal suture impressed dorsally; mesosternum and metasternum without ventral processes; propodeum .declivity with rugosities, declivity and dorsal faces not separated by angles; petiole may have an anterior denticle at the ventral face; postpetiole without ventral tooth.

Pilosity: long hairs (more than .2mm) at thorax dorsum, apex of petiolar and postpetiolar nodes and gaster. Small suberect hairs (.10-.15mm) uniformly distributed on head, legs and sides of thorax and peduncle.

Color: bright brownish-yellow.

Boudinot et al. (2013) - (n=8; 30 from Brandão 1990 in parentheses): HW 1.04–1.15 (0.98–1.03), HL 1.26–1.44 (1.13–1.18), SL 1.48–1.71 (1.50–1.58), OMI 0.27–0.30, EL 0.33–0.38, ML 1.83–2.06 (1.78–1.85), CI 80–83, SI 116–119, EI 31–33, OMI 80–89.

Queen
Boudinot et al. (2013) - Ergatoid (n=1): HW 1.11, HL 1.37, SL 1.55, OMD 0.32, EL 0.36, ML 2.00, CI 81, SI 113, EI 32, OMI 90.

Similar to worker, but differing as follows: all sculpturation rougher and more pronounced; setae stouter and denser on all body surfaces; setal punctures slightly raised, giving the cuticle a less-even shine; promesonotal suture distinct and deeply impressed; petiolar node anteroposteriorly thinner; postpetiolar larger, more globose, with a patch of proprioceptor setae on the anterior face; lateral ocelli present, median ocellus absent.

Male
Boudinot et al. (2013) - (n=5): HW 0.98–1.04, HL 1.02–1.07, SL 0.45–0.47, EL 0.46–0.49, ML 1.85–2.02, CI 96–99, SI 43–46, EI 46–47.

Head Antenna with 13 antennomeres; antennomere 3 apically flattened and kinked; antennomeres 4 and 6 basally kinked; apical antennomeres not forming a club; scape slightly shorter than eye length. Antenna yellow-brown to brown. Palpal formula 3,3, although the apical maxillary palpomere is divided into a thicker basal half and thinner distal half with a suture of variable development. Mandible triangular; masticatory margin with 5–6 teeth; apical tooth more than three times as long as subapical tooth; basal teeth approximately equal in size. Dorsal margin of mandible smooth and shining, with piligerous punctae. Minimum distance between lateral ocellus and compound eye about four times one lateral ocellus length. Compound eye with long ocular setae. Occipital carina visible in full-face view. Mesosoma Mesosoma attenuate. Notauli absent. Parapsidal lines weak. Foraminal carina complete; entire posterior face of propodeum covered with distinct, concentric carinae. Basitarsi tubular. Pterostigma reduced. Forewing crossvein 1m-cu absent; submarginal cell 1 about one fourth to one fifth as wide as long; terminal abscissa of M absent. Metasoma Basipetiolar carina arc-shaped, truncate apically. Ventrolateral carina of petiole absent. Petiolar spiracle just posterad anterior third. Posterior margin of postpetiole with weak to indistinct girdling carinae; postpetiole without girdling carinae. Postpetiolar helcium circular to subcircular. Postpetiolar spiracle placed slightly anterad midlength of postpetiolar lateral tergal margin; not bulging. Sternum of postpetiole convex, bluntly triangular anteroventrally. Postpetiolar tergum globose. Genitalia Abdominal sternum IX broader than long, with obtuse triangular lobe at apex; apical lobe not sclerotized or produced ventrally. Telomere triangular with bluntly rounded apex; dorsal and ventral margins only slightly convex; medial dentiform process absent; medial face and very strongly arched. Cuspis without apicodorsal process. Digitus extremely broad; dorsal margin explanate, strongly arching; ventral margin very weakly curved; ventral margin obscuring posterodorsal angle of cuspis. Valviceps about half as tall as long, subrectangular; dorsal margin sloping steeply to the truncate apex; ventral margin distinctly convex, broadest about midlength; penisvalvar teeth elongate.

Type Material
Boudinot et al. (2013) - Lectotype queen (designated by Brandão 1990: 426): BRAZIL, Rondônia: Porto Velho (not examined). Paralectotype worker: same data (not examined).

References based on Global Ant Biodiversity Informatics

 * Boudinot B. E., T. P. Sumnicht, and R. M. M. Adams. 2013. Central American ants of the genus Megalomyrmex Forel (Hymenoptera: Formicidae): six new species and keys to workers and males. Zootaxa 3732(1): 1-82.
 * Brandão C. R. F. 2003. Further revisionary studies on the ant genus Megalomyrmex Forel (Hymenoptera: Formicidae). Papeis Avulsos de Zoologia (São Paulo) 43: 145-159
 * Fernandes I., and J. de Souza. 2018. Dataset of long-term monitoring of ground-dwelling ants (Hymenoptera: Formicidae) in the influence areas of a hydroelectric power plant on the Madeira River in the Amazon Basin. Biodiversity Data Journal 6: e24375.
 * Kempf, W.W. 1972. Catalago abreviado das formigas da regiao Neotropical (Hym. Formicidae) Studia Entomologica 15(1-4).
 * Longino J. T. 2010. A taxonomic review of the ant genus Megalomyrmex Forel (Hymenoptera: Formicidae) in Central America. Zootaxa 2720: 35-58
 * 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/
 * Silvestre R., M. F. Demetrio, and J. H. C. Delabie. 2012. Community Structure of Leaf-Litter Ants in a Neotropical Dry Forest: A Biogeographic Approach to Explain Betadiversity. Psyche doi:10.1155/2012/306925