Pristomyrmex obesus

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Pristomyrmex obesus
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Crematogastrini
Genus: Pristomyrmex
Species: P. obesus
Binomial name
Pristomyrmex obesus
Mann, 1919

Pristomyrmex obesus casent0281800 p 1 high.jpg

Pristomyrmex obesus casent0281800 d 1 high.jpg

Specimen Labels

Synonyms

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.

A member of the Levigatus species group

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Indo-Australian Region: Solomon Islands (type locality).

Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Biology

The biology of most Pristomyrmex species is poorly known. From Wang (2003): Most species of Pristomyrmex dwell in the rainforest, foraging as predators or scavengers. An Asian species, Pristomyrmex punctatus, however, occurs in open and disturbed habitats (e.g., bare hills, agricultural areas, and beaches). These ants prefer to nest in soil, litter, or rotten wood; in rotten parts of living trees; in dead standing trees; or around plant roots.

Pristomyrmex is of great interest because it exhibits several unusual biological and evolutionary phenomena. The absence of morphologically normal queens and reproduction primarily by unmated workers in P. punctatus {=P. pungens) is a highly unusual life history in the Formicidae. Ergatoid queens, a special wingless female caste morphologically intermediate between the queen and the worker, are present in at least four species: Pristomyrmex punctatus, Pristomyrmex africanus, Pristomyrmex wheeleri, and Pristomyrmex mandibularis; two of them (P. africanus and P. wheeleri) possess both queen and ergatoid queen castes.

Simulating death, slowness of movement, and nocturnal foraging has been recorded in Pristomyrmex (Donisthorpe, 1946; Taylor, 1965; Weber, 1941). Colony size varies greatly among species, ranging from about a dozen to several thousand workers (Donisthorpe, 1946; Itow et al, 1984; Mann, 1919; Taylor, 1965, 1968).

Castes

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • 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.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

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) (Museum of Comparative Zoology, National Museum of Natural History, American Museum of Natural History) [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].

References

  • Mann, W. M. 1919. The ants of the British Solomon Islands. Bull. Mus. Comp. Zool. 63: 273-391 (page 339, worker, queen, male described)
  • Wang, M. 2003. A Monographic Revision of the Ant Genus Pristomyrmex (Hymenoptera:Formicidae). Bull. Mus. Comp. Zool. 157(6): 383-542 (page 509, figs. 233-236, 267, 278 worker, queen, male described, Senior synonym of pegasus and obesus subsp. melanoticus)