Ooceraea siamensis

The single known colony of this species was collected from a fruit orchard near a house, nesting in soil.

Identification
Worker. Body small (head width 0.33–0.38 mm), reddish brown (light brown in some paratypes); antenna 9-segmented; propodeal declivity shallowly concave and encircled with distinct rim; dorsal and lateral faces of head, mesosoma, petiole, postpetiole and abdominal tergite IV (= first gastral tergite) finely and shallowly foveolate; foveae on first gastral tergite smaller than those of head and mesosoma; propodeal declivity smooth and shiny.

Dealate queen. Similar to worker in structure, sculpture, coloration and pilosity, but the body size is slightly larger; eye and ocelli are present.

Ooceraea siamensis is most similar to Ooceraea biroi (see specimen codes CASENT0916710 and CASENT0907059 on AntWeb, 2021) in having a slender body and 9-segmented antenna. However, O. siamensis can be distinguished from O. biroi by the following characteristics: 1) postpetiole slightly longer than broad in dorsal view (clearly shorter than broad in O. biroi); 2) foveae on first gastral tergite and sternite denser and coarser (weak in O. biroi); 3) smaller body size (HW 0.33–0.38 in O. siamensis; 0.46–0.49 mm in O. biroi).

Distribution based on Regional Taxon Lists
Oriental Region: Thailand.

Nomenclature

 * . Ooceraea siamensis Jaitrong et al., 2021: 6, figs. 3, 4 (w.q.) THAILAND.

Type Material

 * Holotype: worker (THNHM-I-02628, THNHM), Thailand: Trang Province, Palian District, Ban Nong Malai, near a house, 23.XII 2018, W. Jaitrong leg., colony no. WJT231218-8.
 * Paratypes: twenty-four workers [SKYC (THNHM-I-19127 and THNHM-I-19128) and THNHM (THNHM-I-19105 to THNHM-I-19126)] and 2 dealate queens (THNHM, THNHM-I-02626 and THNHM I-19104), same data as holotype.