Megalomyrmex modestus

Large polygynous colonies (>2000 workers) have been collected nesting in or under logs and in diffuse soil at the base of trees. Longino (2010) reported a colony ~ 20 cm deep soil on a creek embankment. In a Costa Rican population where Apocephalus phorid flies (B. Brown det.) were seen attacking workers, individuals walked around with their gasters tucked under their bodies. It is difficult to bait this species with Keebler Pecan Sandies as they are mainly subterranean and nocturnal; if the bait is placed on top of a soil nest they will emerge and bury the cookies. Colonies construct soil galleries on the side and at the base of trees when tending immature white flies (Aleyrodoidea: Aleyrodidae). Megalomyrmex modestus was the most frequently collected Megalomyrmex species during Malaise trapping in La Selva, Costa Rica, with well over fifty specimens recovered. (Boudinot et al. 2013)

Identification
Boudinot et al. (2013) - Worker uniquely identified among Central American Megalomyrmex by the following combination: (1) mandible with 5 robust, equally-spaced, subequal triangular teeth; (2) eye small (EL < 0.25); (3) dorsal face of mandible striate; (4) clypeus with triangular median process; (5) disc of katepisternum roughened in ventral half by striations and weak carinulae; (6) petiolar peduncle long and thin. Queen similarly identifiable as worker, but alate, with larger eyes, and less-robust petiolar and postpetiolar nodes. Male uniquely identified among Central American Megalomyrmex by either of the following: (1) postpetiolar helcium laterally compressed; (2) telomere with a dorsomedian dentiform process. Otherwise recognized by the following combination: (1) forewing 1m-cu present; (2) scape length less than antennomeres 2–4; (3) occipital carina visible in full-face view; (4) mesosoma robust.

Workers, alate queens, and males of Megalomyrmex modestus have relatively dense, short ocular setae. Meglomyrmex modestus workers are set off from the Central American leoninus- and modestus-group species by several traits unique in this two groups: (1) body comparatively small (ML 1.40–1.65 vs. ML 1.83–2.71); (2) eyes relatively small (EI 20–21 vs. EI 25–33); (3) dorsal mandibular face striate (vs. smooth); (4) anterior clypeal margin strongly angulate medially (vs. weakly dentate or convex); (5) antennal club distinctly broader than preceeding antennomeres of funiculus (vs. subequal in width to preceeding antennomeres); (6) gastral shoulders strong (vs. weak or indistinct); petiolar peduncle long and thin (vs. comparatively shorter and stout); and body completely pale yellow (vs. head and mesosoma orange and/or gaster black). However, given these distinct characters, it is notable that M. modestus shares with Megalomyrmex wallacei (another modestus group species) a notch between the basalmost and basal mandibular margins.

Key to Central American Megalomyrmex:
 * workers
 * males

Distribution
Sea-level to 940 m elevation.

Distribution based on Regional Taxon Lists
Neotropical Region: Colombia, Costa Rica, Ecuador, Panama, Venezuela.

Biology
Longino (2010): Forel (1899) reported that the type specimens were collected by A. Alfaro from a rotten log. Kugler collected specimens in Colombia, from a “large nest in rotten log, soil - rocks, under forest” (reported in Brandão 1990).

In Costa Rica, M. modestus is found in mature wet forest of the Atlantic slope. Although it occurs at sea level, it is most abundant at middle elevations, 500–800 m. Nests are subterranean and very large. From these nests, inconspicuous covered galleries extend large distances up trees and under liana stems, and workers may be found under epiphyte mats in the canopy. Workers tend Coccoidea under the shelters. Workers are occasionally collected at baits on the forest floor, but in general they are not often seen as exposed foragers.

At Refugio Eladio, on the Río Peñas Blancas, I found a nest on the bank of a small stream. An area of excavated soil about 2m across covered the ground. There were hundreds of small entrances, and excavations in the surface soil turned up only scattered workers, and no brood. As I dug deeper into the center of the nest (more than 20cm deep) workers became more dense and I began finding adult males and some brood. At a depth of about arm's length workers were very dense, brood more abundant, and two dealate queens were turned up. The soil was very friable, and I could not discern any gallery or chamber structure. Given that I was digging in only a small part of the colony, and turned up two queens, the colony must have had many queens. Around the periphery of the colony there were abundant Coccoidea (Pseudococcidae?) in the soil.

Nomenclature

 *  modestus. Megalomyrmex modestus Emery, 1896g: 94 (w.) COSTA RICA. Brandão, 1990: 426 (q.m.).

Male
(n=2): HW 0.87–0.89, HL 0.83, SL 0.27, EL 0.43–0.45, ML 1.60–1.64, CI 105–107, SI 33, EI 49–51.

Head Antenna with 13 antennomeres, none of which are kinked, nor forming a club; scape length shorter than eye length. Entire antenna brown, except apex of terminal antennomere which is pale. Palpal formula 4,3. Mandible subfalcate; masticatory margin with three triangular teeth; apical tooth about twice the length of the subbasal tooth; subbasal tooth subequal in size to basal tooth from which it is separated by a short diastema. Dorsal face of mandible striate, at least at midlength. Minimum distance between lateral ocellus and compound eye about three lateral ocellus lengths. Compound eyes with dense, short ocular setae. Occipital carina visible in full-face view. Mesosoma Mesosoma robust. Notauli absent. Parapsidal lines weak. Foraminal carina present. Metasternum with a triangular process. Basitarsi tubular. Pterostigma elongated apically. Forewing crossvein 1m-cu present; submarginal cell 1 one fourth as wide as long; terminal abscissa of M branches from Rs at or just basad 2r-rs. Metasoma Basipetiolar carina arc-shaped; weak; most distinct laterally, obsolescent medially. Ventrolateral longitudinal carina of petiole present. Petiolar spiracle in anterior fourth. Posterior margin of petiole with distinct girdling carinae; postpetiole without. Postpetiolar helcium strongly compressed laterally. Postpetiolar spiracle placed about midlength of the lateral tergal margin. Sternum of postpetiole produced anteriorly; this process angular, sloping gently to posterior margin. Genitalia Abdominal sternum IX lateral margins subparallel, arching apically to posterior margin which is ventromedially produced as a relatively strongly sclerotized apical triangle; this triangle is keeled ventrally and produced apically; lateral faces of this apical triangle concave. Telomere triangular, elongate, with apex acutely angled; telomere with medially-directed dentiform process (hence “shouldered”); medial face of telomere sclerotized, arched; ventral margin with two anteriorly-directed sclerotized denticles. Cuspis with posterodorsal process; apical margin weakly convex. Digitus narrow; dorsal margin explanate, with posterodorsal margin subangular; ventral margin parabolic; apex triangular; ventral margin slightly obscuring apex of cuspal posterodorsal process. Valviceps about half as tall as long, subrectangular; dorsal margin curving smoothly through apical margin to meet the sclerotized ventral margin; basal two thirds of ventral margin linear; penisvalvar teeth short, truncate, close-set.

Type Material
Boudinot et al. (2013) - Lectotype worker (designated by Brandão 1990: 425): COSTA RICA: Suerre [near Jimenez, Limón Prov.] (not examined).