Pristomyrmex obesus

This species has been collected in forest litter. Mann (1919) found a colony composed of less than a dozen workers, a dealated queen, and one male under a stone.

Identification
Wang (2003) - Worker. Masticatory margin of mandible lacking a diastema and possessing four teeth, of which the third tooth, counting from the apex, smallest; eyes containing four to seven ommatidia in the longest row; dorsum of head, except for the scrobes, usually with dense foveolate punctures; entire first gastral tergite evenly cove red with numerous erect or suberect hairs.

Pristomyrmex obesus occurs on Solomon Is. It is similar in the workers to Pristomyrmex simplex of New Guinea but can be separated from the latter by possessing numerous erect or suberect hairs evenly distributed on the entire first gaster tergite. In the levigatus group, this character is present only in two species, Pristomyrmex obesus and Pristomyrmex longus; in the other species, the first gastral tergite has a few or no hairs. In addition, foveolate punctures on the dorsal head are denser in the workers of P. obesus than in P. simplex.

Key to Pristomyrmex workers

Distribution based on Regional Taxon Lists
Indo-Australian Region: Solomon Islands.

Nomenclature

 * melanoticus. Pristomyrmex obesus subsp. melanoticus Mann, 1919: 340 (w.) SOLOMON IS. Junior synonym of obesus: Wang, M. 2003: 509.
 *  obesus. Pristomyrmex obesus Mann, 1919: 339 (w.q.m.) SOLOMON IS. Senior synonym of melanoticus, pegasus: Wang, M. 2003: 509.
 * pegasus. Pristomyrmex pegasus Mann, 1919: 338, fig. 27 (w.) SOLOMON IS. Junior synonym of obesus: Wang, M. 2003: 509.

Worker
Wang (2003) - TL 2.24-3.22, HL 0.63- 0.86, HW 0.61-0.86, CI 94-104, SL 0.52-0.75, SI 79-88, EL 0.09-0.14, PW 0.41-0.55, AL 0.58- 0.88, PPW 0.18-0.24, PPL 0.16-0.20, PPI 10.5-12.5 (n = 90).

Mandibles usually smooth and shining but sometimes with a few superficial short rugae or a few hair pits. A broad-based triangular short tooth present about midway on the basal margin of the mandible. Clypeus flat, smooth, but the median carina of frontal area usually extending to the clypeus. Anterior clypeal margin with a median denticle and two lateral teeth, but the median denticle often smaller than the others; sometimes the median denticle lacking; thus, only two teeth are present there. Ventral surface of clypeus lacking toothlike prominences or rugae. Palp formula 1,3. Frontal carinae extending to the level of the posterior margins of eyes. Scrobal impressions broad, shallow, present lateral to the frontal carinae. Frontal lobes slightly expanded. Eyes moderately sized, usually containing five to seven (rarely four) ommatidia in the longest row. Pronotum unarmed. Propodeum with a pair of triangular short spines. Metapleural lobes rounded. Dorsum of alitrunk in dorsal view usually with a longitudinal impression or furrow at middle, but sometimes this longitudinal impression indistinct. Petiole node in profile high with the anterodorsal angle higher than the posterodorsal, its anterior peduncle nearly as long as the node. Subpetiole with a narrow semitranslucent lamella. Postpetiole in profile rounded dorsally. In dorsal view, dorsum of petiole node sub rounded, about as long as broad; postpetiole somewhat transversally rectangular and slightly broader than long. Dorsum of head, except for the scrobes, usually with dense foveolate punctures. Dorsum of alitrunk with scattered foveolate punctures. Petiole, postpetiole, and gaster smooth and shining. Dorsal surfaces of head and alitrunk with numerous erect to suberect long hairs. Two pairs of hairs usually present on the dorsum of petiole node and two to three pairs usually on the dorsum of postpetiole. Entire first gastral tergite covered with numerous, evenly distributed erect or suberect hairs. A few pairs of forward-projecting hairs present near the anterior clypeal margin. Scapes and tibiae with numerous erect to suberect short hairs. Color reddish-brown.

Queen
Wang (2003) - TL 2.69-3.40, HL 0.69-0.82, HW 0.67-0.85, CI 97-104, SL 0.54-0.68, SI 78-85, EL 0.15-0.19, PW 0.54-0.64, AL 0.76-0.94, PPW 0.20-0.26, PPL 0.18-0.22, PPI 111-122 (n = 15).

Generally similar to worker, except for caste differences. In addition, foveolate punctures shallow on the mesonotum; propodeal armaments slightly shorter than those in the conspecific workers; dorsum of alitrunk lacking a longitudinal furrow.

Male
Wang (2003) - A syntype male, together with about a dozen workers and a queen, collected in Fulakora, Solomen I., by W. M. Mann on 19.v.-24.xi.1916, constitutes a series. A second male specimen, together with five workers, collected in Guadalcanal, Solomen I., by P. Greenslade, constitutes another series. Each of the two males was originally mounted with two or three workers, respectively, on the same pin. TL 2.92; HL 0.52, 0.53; HW 0.53, 0.54; CI 102, 102; SL 0.20, 0.22; SI 38, 41; HWE 0.66, 0.68; EL 0.2.5, 0.26; PW 0.58, 0.60; AL 0.90, 0.92; PPW 0.18; PPL 0.18; PPI 100 (n = 2).

Head, including the eyes, broader than long. Clypeus convex, without a median longitudinal carina. Anterior clypeal margin transverse. Frontal carinae weak or indistinct. On the mesoscutum, notauli distinct, forming a Y shape; parapsidal furrows absent. Scuto-scutellar sulcus rather broad, with five narrow longitudinal ridges. Propodeum weakly tuberculate, lacking teeth and spines. Metapleural lobes somewhat rounded. Petiole node in profile low, rounded dorsally. Postpetiole in profile low, rounded dorsally, in dorsal view subquadrate. Dorsum of head unsculptured and shining, except for a median longitudinal carina present on the frontal area. Dorsal surface of alitrunk smooth and shining but with well-marked sutures. Petiole, postpetiole, and gaster smooth and shining. Dorsal surfaces of head, alitrunk and gaster with abundant long hairs. Legs with numerous hairs. Body blackish-brown; wings infuscated.

Type Material
Wang (2003):

Syntype workers, queen and male, Solomon Is.: Ysabel, Fulakora; Malaita, Auki; Three Sisters, Malapaina; 19,v.-24.xi.1916 (W. M. Mann) [examined].

Pristomyrmex pegasus Holotype worker, Solomon Is.: Santa Cruze: Graciosa Bay, 19.v.-24.xi.1916 (W. M. Mann) (USNM) [examined].

Pristomyrmex obesus melanoticus Syntype workers, Solomon Is.: San Cristoval, Pamua; Wai-ai; 19.v.-4.xi.1916 (W. M. Mann) (MCZC, USNM) [examined].