Aenictus silvestrii

Specimens from Sabah were found marching on the forest ﬂoor in a primary rainforest.

Identification
A member of the silvestrii species group. Aenictus silvestrii is very unique in having the head and mesosoma with rugae which are absent in the other species of the group, but it has the same number of antennal segments (9) as has Aenictus jarujini.

Distribution
Malay Peninsula and Borneo (Sabah and Brunei)

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

Castes
Known only from the worker caste.

Nomenclature

 *  silvestrii. Aenictus (Paraenictus) silvestrii Wheeler, W.M. 1929g: 28, fig. 1 (w.) WEST MALAYSIA. See also: Wilson, 1964a: 479; Jaitrong & Yamane, 2010: 331.

Description
Jaitrong and Yamane (2010) - The measurement of a syntype after Wilson (1964): HL 0.92 mm; HW 0.83 mm; SL 0.59 mm. HW of 2nd syntype 0.80 mm. Nontype material (n = 4): TL 3.9–4.1 mm; HL 0.87–0.93 mm; HW 0.82–0.85 mm; SL 0.50–0.57 mm; ML 1.25–1.3 mm; MTL 0.6–0.63 mm; PL 0.30–0.35 mm; CI 89–94; SI 61–70. Head in full-face view subrectangular, slightly longer than broad, with feebly convex sides; posterior margin of head almost straight but weakly sinuate; occiput bearing a narrow collar with irregular carinae. Antenna 9-segmented (in some nontype specimens segment III is clearly demarcated from IV, though in the two syntypes this segmentation is not very clear); antennal segment II small, nearly as long as broad; III very short, broader than long; IV nearly as long as broad; V and VI distinctly longer than broad; VII and VIII as long as broad; the last (IX) longer than broad and much longer than others, almost as long as VII and VIII combined. Frontal carinae short extending less than half length of head, very poorly developed in posterior half. Clypeus short and roundly produced anteriorly, lacking anterior teeth. Mandible with apical tooth large and curved, followed by a series of 10–15 denticles of two sizes, the larger alternating with 2–3 of smaller; basal margin of mandible with 3–4 small denticles. With mesosoma seen in profile promesonotum weakly convex dorsally and sloping gradually to metanotal groove; dorsal outline of propodeum almost straight. Propodeal junction acutely angulate; declivity of propodeum shallowly concave, encircled with a rim. Petiole slightly longer than broad, relatively low, nearly as high as long, anteriorly and posteriorly margined with a rim similar to that of propodeum but poorly developed; subpeiolar process very low; postpetiole as long as petiole in profile roundly convex above, anteroventrally produced as a blunt angle directed downward and forward. Gaster elongate-elliptical, narrowed anteriorly and posteriorly.

Head extensively with regular rugae and dense minute punctures on rugae; rugae on lateral and ventral faces of head longitudinal, but those on vertex transverse and those on frons curved outwardly. Mandible except in apical portion and along masticatory margin, and antennal scape wholly with dense small punctures. Dorsum of mesosoma, pro-and mesopluron with regular longitudinal rugae. Node of petiole with irregular longitudinal carinae and dense small punctures; postpetiole with similar sculpture but carinae weaker than on petiole.

Gaster smooth and shining except for extreme base. Fore coxa distinctly punctate; narrow basal portions of femora distinctly sculptured and mat; other parts of legs largely smooth.

Body with relatively sparse standing hairs mixed with sparse short hairs over the surface; length of the longest pronotal hair approximately 0.20 mm. Head, mesosoma and waist reddish brown to dark brown; mandible dark brown; antenna reddish brown, with the apical segment paler; gaster and legs largely yellowish brown; narrow basal potions of femora darkened.

Type Material
Jaitrong and Yamane (2010) - Two syntype workers from Penang Island, Malay Peninsula deposited in (examined).

References based on Global Ant Biodiversity Informatics

 * Jaitrong, W.; Yamane, S. 2010. The army ant Aenictus silvestrii and its related species in Southeast Asia, with a description of a new species (Hymenoptera: Formicidae: Aenictinae). Entomological Science 13:328-333.
 * 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