Odontomachus rixosus Smith, 1857

Sorger, D. M. & Zettel, H., 2011, On the ants (Hymenoptera: Formicidae) of the Philippine Islands: V. The genus Odontomachus Latreille, 1804., Myrmecological News 14, pp. 141-163 : 157

Odontomachus rixosus Smith, 1857 (Figs. 40 - 42, 47)

Odontomachus rixosus Smith, 1857: 64 (description of worker; type locality: Singapore).

Odontomachus rixosus var. obscurior Forel, 1900 : Stitz 1925: 115 (distribution: Binaluan, Palawan) (syn. Brown 1976).

Material from the Philippines examined (34 workers; CSW, NHMW, UPLB): Palawan: Mt. Mantalingajan, Pinigisan, 600 m, 11.IX.1961, Noona Dan Expedition, 1 ∑. Mindanao: Surigao del No rte: SW Bacuag, Payapag, Little Baguio Waterfalls, 6.II.2000, leg. S. Schödl (9), 33 ∑∑.

Material from other countries examined: 105 workers, 9 gynes (CZW, NHMW) from Myanmar (Tenasserim), Thailand, (North, East, Central, South), Malaysia (Peninsular, Sarawak, Sabah), and Indonesia (Sumatra, Mentawai).

Description of worker: Measurements: worker with smallest HW: CI 71, HL 2.38, HW 1.68, MdI 57, MdL 1.37, MsL 3.33, PnW 1.05, PtH 0.78, PtL 0.77, PtW 0.42, SI 145, SL 2.43, TL 10.31; worker with largest HW: CI 76, HL 2.57, HW 1.95, MdI 56, MdL 1.43, MsL 3.62, PnW 1.17, PtH 0.84, PtL 0.92, PtW 0.48, SI 131, SL 2.63, TL 12.94.

Structures: Mandibles long, with ca. 6 basal denticles (widely separated from each) and three apical teeth: proximate tooth truncated, intercalary tooth only slightly shorter than apical. Head rectangular, broadest at level of eyes. Striation on head until ocular ridge, some more striation between ocular and temporal ridge, rest of head smooth and shiny. Microsculpture on head with fine isodiametric reticulum. Mesosoma elongate, slender and low, broadest at level of pronotum. Pronotum rounded, metanotal groove in lateral view present. Coarse rounded sculpture on pronotum (closed circles visible in dorsal view), metanotum and propodeum with coarse transverse sculpture. Petiole short, smooth and shiny, almost conical, with very short petiolar spine, which is rarely absent in small specimens (for example, O. rixosus var. conifera Forel, 1913 ).

Pilosity: Fine loose semi-appressed white pubescence on head, mesosoma and petiole; distance between hairs approximately their length. Head with two standing setae, tergite 1 without setae, tergite 2 with a few setae, number of setae and length increasing towards apex of abdomen.

Colour: Medium brown, mesosoma slightly darker than head, petiole and gaster.

Distribution: (Philippines: Fig. 47) Southeast Asian mainland (Myanmar, Thailand, Peninsular Malaysia, Singapore), Sumatra, Mentawai Islands, Java, Borneo (Brown 1976, and new material listed above). Brown (1976) specifically noted the absence of O. rixosus from the Philippines, but overlooked the record of O. rixosus var. obscurior - a taxonomically insignificant colour variation - by Stitz (1925) from Palawan. This record is also lacking in BALTAZAR's (1966) catalogue. In the material we examined we found more specimens from Palawan and one record from northeastern Mindanao.

Habitats: The only encounter in the Philippines by the senior author was at a waterfall area in a slightly degraded dipterocarp forest. Observations from Borneo confirm that O. rixosus is a forest species.

Notes: There is considerable variation in O. rixosus , especially in size and colour, but it seems unconnected with certain geographical populations. This includes the var. obscurior, described from Myanmar and Thailand (Forel 1900), and later recorded from Palawan by Stitz (1925).

In the Philippines, O. rixosus can be recognized by group characters, especially by the elongate and truncate subapical tooth of the mandible.