Megalomyrmex miri

In May 2010, a large colony of Megalomyrmex miri was found cohabiting with Myrmicocrypta ednaella (J. Sosa-Calvo det.) confirming M. miri as a guest ant and social parasite. The host colony had ~108 workers and a single queen, while the M. miri colony had ~144 workers, four queens, and two males. This is the first record of a Megalomyrmex species parasitizing Myrmicocrypta. Few behavioral observations were possible but amiable interactions between host and parasites were most common. Gaster flagging by M. miri workers was observed on occasion. Attempts were made to introduce this species into Cyphomyrmex longiscapus Weber colonies (host of Megalomyrmex wettereri) with marginal success. (Boudinot et al. 2013)

Identification
Boudinot et al. (2013) - Worker distinguished by the following: (1) miniscule eyes, with at most four ommatidia at greatest diameter; (2) disc of katepisternum costate. See distinctions from M. wettereri below for more characters. Queen Alate; distinguished by the following: (1) ventral petiolar faces rugose; (2) dorsal and posterior propodeal faces meeting at a distinct angle. Male recognizable as follows: (1) forewing 1m-cu present; (2) occipital carina not visible in full-face view; (3) petiolar and postpetiolar sterna scabrous; (4) scapes distinctly shorter than head width.

Characters which separate the workers of M. miri from Megalomyrmex wettereri are as follows: (1) smaller (HL 0.49–0.55 vs. 0.58–0.59); (2) scape longer (SI 90–96 vs. 84–85); (3) setae on scape appressed (vs. decumbent to subdecumbent); (4) katepisternum longitudinally costate (vs. smooth); (5) petiolar peduncle with a dorsolateral longitudinal carina extending about one-fifth the length of the node (vs. without); (6) posterior face of petiolar node meeting posterior petiolar collar at a distinct angle (vs. smoothly curving through petiolar collar to posterior petiolar margin); (7) petiolar sternum almost completely rugose (vs. smooth and “polished”); (8) first gastric tergum with long, relatively dilute decumbent to subdecumbent setae interspersed with shorter appressed setae; (9) setae on legs appressed (vs. subdecumbent to decumbent); (10) head with distinct appressed and subdecumbent setae (vs. setae grading from decumbent to subdecumbent). Queens share with workers at least characters 2, 3, 5, 6, 7, 8, 9, 10.

Males of M. miri may be separated from those of M. wettereri by the following gross morphology: (1) scape setae completely appressed (vs. appressed to decumbent); (2) setae on legs, excluding ventral faces, completely appressed (vs. appressed to subdecumbent); (3) petiolar and postpetiolar nodes stronger, taller; (4) petiolar sternum rugose; (5) postpetiolar sternum anteriorly dentate in profile view (vs. rounded). In addition to gross morphology, several genitalic characters separate the two closely related species: (1) dorsal margin of telomere concave; (2) apical segment of digitus thinner than digitus stem, linear; (3) apicodorsal margin of cuspis obscured by digitus stem; (4) apical margin of cuspis emarginate; (5) penisvalvar teeth distinctly separated; (6) ventral margin of penisvalva convex; (7) penisvalva shorter. Morphometrically, males of M. miri and M. wettereri differ only slightly. A larger sample size for the respective species may yield further discriminatory characters.

Distribution
Costa Rica and Panama; sea-level to 400 m elevation.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Costa Rica, Panama.

Nomenclature

 *  miri. Megalomyrmex miri Brandão, 1990: 452, figs. 117, 118 (w.) COSTA RICA.

Worker
Brandão (1990) - Smooth mandibles with 2 apical teeth and 5-6 subapical denticles; anterior clypeal border round without median denticle: 5 ocular facets at compound eyes largest diameter; frontal suture not impressed; occipital margin not raised; promesonotum profile continuous; metanal groove deeply excavated and completely sculptured; dorsal face and declivity of propodeum meeting in marked and divergent angles; declivity with faint concentric rugosities; epipetiolar carina complete: petiolar node compressed anteroposteriorly; ventral face of petiole with blunt anterior denticle originating a transversally sculptured flange; ventral face of postpetiole with a small acute tooth.

Pilosity: short apressed hairs at scape (less than .I mm): frontal carina, head vertex, and sides of pronotum with hairs of circa. .lmm; pronotum dorsum and apex of petiolar and postpetiolar nodes and gaster with longer hairs (between .15 and .2mm).

Color: bright light yellow with translucid gaster.

Queen
Boudinot et al. (2013) - Measurements (n=1): HW 0.55, HL 0.59, SL 0.53, OMD 0.09, EL 0.18, ML 0.93, CI 93, SI 90, EI 32, OMI 51.

Differs from worker as follows: eye proportionally larger; ocelli present; mesosoma with alate condition, disc of katepisternum smooth; petiole and postpetiole more robust.

Male
Boudinot et al. (2013) - (n=1): HW 0.46, HL 0.48, SL 0.25, EL 0.24, ML 0.88, CI 95, SI 52.

Head Antenna with 13 antennomeres, none of which are kinked, nor forming a club; scape length greater than eye length. Antenna pale yellow grading to honey yellow apically. Mandible triangular; masticatory margin with five teeth; apical tooth largest, about four times as long as basal teeth; basal four teeth equal in size and evenly spaced. Dorsal face of mandible densely and finely striate. Minimum distance between lateral ocellus and compound eye about four lateral ocellus lengths. Compound eye with extremely sparse, short ocular setae. Occipital carina not visible in full-face view. Mesosoma Mesosoma not attenuate. Notauli absent. Parapsidal lines distinct. Foraminal carina incomplete; posterior face of propodeum smooth. Basitarsi tubular. Pterostigma well-developed. Forewing with crossvein 1m-cu; submarginal cell 1 length about four times width; terminal abscissa of M branching from Rs+M near 2r-rs, becoming spectral near its base, becoming absent well before apical margin. Metasoma Basipetiolar carina arc-shaped. Ventrolateral carina of petiole indistinct. Petiolar spiracle in anterior fourth of petiole. Petiolar and postpetiolar posterior margins without distinct girdling carinae. Postpetiolar helcium circular. Postpetiolar spiracle anterad midlength lateral margin of tergum. Sternum of postpetiole with an acute anterior denticle. Postpetiolar tergum strongly convex. Genitalia Abdominal sternum IX tapering to long acute triangular lobe at apex; apical lobe not heavily sclerotized or produced ventrally. Telomere triangular with blunt apex; dorsal margin concave, ventral margin linear; medial dentiform process absent; medial face distinctly sclerotized, subquadrate, very weakly arched. Cuspis produces apicodorsally; apical margin sinuate. Digitus apical portion very thin (thinner than digitus stem); dorsal margin strongly and narrowly explanate posteroapically; ventral margin evenly curved; ventral margin obscuring posterodorsal angle of cuspis. Valviceps height just subequal to length, ovate; dorsal margin curving sharply to ventral margin at apex; ventral margin weakly convex basally; penisvalvar teeth distinctly separated, longest near base.

Type Material
Zent. Costa Rica (10° 02'N, 83° 16'W). Holotype at National Museum of Natural History, Washington; Paratype at Museu de Zoologia da USP.The type specimens bear a label saying “W. M. Mann collection 1954” and have been collected in March. 1924.

Etymology
The small size suggested the Tupi name miri.

References based on Global Ant Biodiversity Informatics

 * Brandão C. R. F. 1990. Systematic revision of the Neotropical ant genus Megalomyrmex Forel (Hymenoptera: Formicidae: Myrmicinae), with the description of thirteen new species. Arquivos de Zoologia (São Paulo) 31: 411-481
 * 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