Aenictus siamensis

Aenictus siamensis is found in highland (700–900 m alt.) seasonal forests (hill evergreen forest and dry evergreen forest) and open areas. A colony from Loei Province was collected at night, a colony from Chiang Mai Province during the day. The type series and a colony from Doi Suthep-Pui National Park, Chiang Mai Province were collected using pitfall traps.

Identification
Jaitrong and Yamane (2011) - A member of the laeviceps species group.Aenictus siamensis is similar to Aenictus binghami in having the mesosoma extensively sculptured, but is much smaller than the latter. Furthermore the pronotal sculpture is much weaker (dorsum almost smooth) in the latter.

Key to Aenictus species groups / Key to Aenictus laeviceps group species

Distribution based on Regional Taxon Lists
Oriental Region: Thailand.

Castes
Known only from the worker caste.

Nomenclature

 *  siamensis. Aenictus siamensis Jaitrong & Yamane, 2011: 42, figs. 35-37 (w.) THAILAND.

Worker
Measurements. Holotype and paratypes (n = 10): TL 3.75–3.90 mm; HL 0.78–0.85 mm; HW 0.63–0.70 mm; SL 0.68–0.75 mm; ML 1.18–1.25 mm; PL 0.25–0.28 mm; CI 81–82; SI 107–108.

Holotype and paratypes - Head in full-face view distinctly longer than broad, with sides convex and posterior margin almost straight; occipital carina complete. Antennal scape relatively long, reaching the posterolateral corner of head; antennal segments II–X each longer than broad; II almost as long as each of III–VI. Frontal carina very short, not extending beyond the level of posterior margin of torulus. Anterior margin of clypeus convex, bearing 8–9 denticles. Masticatory margin of mandible with a large apical tooth followed by a medium-sized subapical tooth, 6–7 denticles, and often 1 or 2 small basal teeth; basal margin lacking denticles. Mesosoma relatively slender; promesonotum in profile weakly convex dorsally and sloping gradually to metanotal groove; dorsal outline of propodeum feebly convex; propodeal junction angulate; declivity shallowly concave, encircled by a thin rim. Petiole subsessile, its node almost as long as high with strongly convex dorsal outline; subpetiolar process well developed and triangular with apex directed downward; postpetiole almost as long as petiole, the node similar to that of petiole in shape.

Entire head smooth and shiny. Mandible very finely striate except along masticatory and outer margins. nal scape superficially sculptured and shiny. Pronotum dorsally almost smooth and shiny; lateral face superficially reticulate and weakly shiny; mesothorax, metapleuron and propodeum densely punctate; mesothorax and propodeum often with ill-defined longitudinal rugulae on lateral faces. Petiole with dense small punctures; postpetiole entirely smooth and shiny. Legs extensively smooth and shiny.

Head and mesosoma dorsally with relatively sparse standing hairs mixed with sparse short hairs over the surface; longest pronotal hair 0.23–0.27 mm long. Entire body dark reddish brown. Typhlatta spot located anterior to occipital corner.

Type Material
Holotype worker from NE. Thailand, Chaiyaphum Prov., Phu Kheao Dist., Hill evergreen forest, 27 III 1999, W. Jaitrong leg., WJT99-TH55. Eighteen paratype workers, same data as holotype (,, , , , THNHM).

Etymology
The specific name is an adjective meaning ‘of Siam (old name of Thailand)’.