Pheidole acantha

This species inhabits well-developed forest on Mt. Kinabalu from 1500-1800 m alt., and nests in rotting wood.

Identification
Eguchi et al. (2001) - Distinctive from Pheidole leloi: In the major, promesonotal dome with a conspicuous transverse ridge on its posterior slope; ventral face of petiole without a longitudinal carina. In the minor, dorsum of mesosoma in profile bearing less than 10 standing hairs.

Eguchi (2001) - P. acantha is closely related to Pheidole lokitae, Pheidole quadrensis, Pheidole sperata, Pheidole quadricuspis and Pheidole spinicornis., and several undescribed species (see under P. lokitae), but can be recognised among the Bornean relatives by the characters given in the key. Also see the drawing in the nomenclature section.

Sculpture of head in both the subcastes is generally weaker in the specimens from an elevation of ca. 1800 m than in those from that of ca. 1500 m on Mt. Kinabalu.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Indonesia, Malaysia.

Nomenclature

 *  acantha. Pheidole acantha Eguchi, 2001b: 25, fig. 3 (s.w.q.) BORNEO.

Worker
Major. (n=5): TL 4.3-5.3 mm, HL 1.98-2.37 mm, HW 2.13-2.50 mm, SL 1.17-1.27 mm, FL 1.63-1.88 mm, CI 101-107, SI 48-58, FI 71-87. Head broadest at about 2/3 distance of head (as measured from the mid-point of a transverse line spanning the anteriormost and posteriormost projecting points, respectively (cf. Fig. 2A»; posterior margin of head weakly concave in full-face view (Fig. 3A); head in profile not impressed on vertex (Fig. 3B). Hypostoma with a pair of stout median processes. Clypeus with a median longitudinal carina, with anterior margin emarginate medially. Eye situated at about 1/3 distance of head; distance between mandibular insertion and anterior margin of eye 1.7-1.9 times as long as maximal diameter of eye. Frontal carina inconspicuous, extending backward to about midlength of head. Antennal scrobe present only around antennal insertion. Antenna with 3-segmented club; scape reaching about 3/5 distance of head; terminal segment almost as long as preceding two segments together. Masticatory margin of mandible with apical and preapical teeth, and a denticle in front of basal angle. Promesonotal dome with a pair of dorsolateral spines, which are slender, sharp, with narrow base; posterior declivity of the dome with a distinct prominence (Fig. 3C); the prominence in anterior view not or very weakly concave medially. Mesopleuron with an inconspicuous transverse impression. Propodeal spine horn-like, with narrow base, ca. 5 times as long as diameter of propodeal spiracle. Petiole cuneiform, ca. 1.4 times as long as postpetiole (excluding helcium); petiolar node in profile acute (Fig. 3C), and in posterior view emarginate at apex; subpetiolar process absent. Postpetiole 1.9-2.2 times as broad as petiolar node, in profile usually angulate anteroventrally.

Frons and gena longitudinally rugose; vertex, and dorsal and lateral faces of occipital lobe reticulate; alitrunk irregularly rugoso-reticulate; lateral face of petiole weakly punctured; dorsum of petiole, and postpetiole largely smooth and shining; gaster largely smooth and shining, or weakly punctured on anterior half of first gastral tergite. Outer face of mandible sparsely covered with appressed to decumbent hairs which are 0.07-0.12 mm in length and (a little) longer than distance between piligerous punctures. Body brown to dark reddish-brown, with darker head (and abdomen); antennae and legs brown, lighter than alitrunk.

Minor. (n=5): TL 2.8-3.3 mm, HL 0.88-1.00 mm, HW 0.76-0.91 mm, SL 1.17-1.26 mm, AL 1.23-1.43 mm, FL 1.28-1.47 mm, CI 86-93, SI 139-153, FI 160-168. Head in full-face view oval (Fig. 3D), with distinct occipital carina. Clypeus with a median longitudinal carina, with anterior margin in full-face view weakly convex medially. Eyes situated at about midlength of head; distance between mandibular insertion and anterior margin of eye 1.2-1.3 times as long as maximal diameter of eye. Frontal carina and antennal scrobe present only around antennal insertion. Antenna with 3-segmented club; in full-face view scape extending beyond posterior border of head by more than its 1/3 length; terminal segment 0.9-1.0 times as long as preceding two segments together. Promesonotal dome with a pair of dorsolateral spines, with a weak prominence on its posterior declivity (Fig. 3E). Mesopleuron without a transverse impression. Propodeal spine horn-like, with narrow base, 4-5 times as long as diameter of propodeal spiracle. Petiole cuneiform, ca. 1.2 times as long as postpetiole (excluding helcium); petiolar node in profile acute (Fig. 3E), and in posterior view emarginate at apex. Postpetiole 2.0-2.3 times as broad as petiolar node.

Clypeus smooth and shining with a few rugulae; remainder of head rugoso-reticulate; area between promesonotal spines smooth and shining; remainder of alitrunk punctured, or weakly reticulate with punctured enclosures; lateral face of petiolar pedicel very weakly punctured; dorsum of petiole, and postpetiole and gaster smooth and shining. Dorsum of alitrunk in profile bearing less than 10 standing hairs. Body colour pattern similar to that of the major.

Type Material
Holotype Major, colony: Eg97-BOR-404, Mt. Kinabalu (near the Headquarter, ca. 1500 m alt.), Sabah, E. Malaysia (Borneo), K. Eguchi leg., 1997, deposited in. Paratypes 4 majors, 10 minors and 1 queen from the same colony to which the holotype belongs, deposited in, , , and UMS.

References based on Global Ant Biodiversity Informatics

 * Eguchi K. 2001. A revision of the Bornean species of the ant genus Pheidole (Insecta: Hymenoptera: Formicidae: Myrmicinae). Tropics Monograph Series 2: 1-154.
 * Eguchi K., B. Tuan Viet, E. Oguri, and S. Yamane. 2016. The first discovery of the “Pheidole quadricuspis group” in the Indo-Chinese Peninsula (Insecta: Hymenoptera: Formicidae: Myrmicinae). Revue suisse de Zoologie 123(1): 45-55.
 * Eguchi, K. "A revision of the Bornean species of the ant genus Pheidole (Insecta:Hymenoptera:Formicinae:Myrmicinae)." Tropics Monograph Series 2 (2001): 1-154.
 * Pfeiffer M.; Mezger, D.; Hosoishi, S.; Bakhtiar, E. Y.; Kohout, R. J. 2011. The Formicidae of Borneo (Insecta: Hymenoptera): a preliminary species list. Asian Myrmecology 4:9-58
 * Sukimin S., M. Mohamed, and H. Aris. 2010. Ant diversity of Maliau Basin Conservation Area, Sabah, Malaysia. Journal of Tropical Biology and Conservation 6:89-101.