CHINA, Yunnan, Xishuangbanna: XTBG (21.917°N, 101.274°E), Rain forest, 05.vi.2013, 1 major worker, 552 m, Winkler sifting, B. Guénard, B. Blanchard and C. Liu; XTBG (21.918°N, 101.270°E), Rain forest, 05.vi.2013, 3 workers, 581 m, Winkler sifting, B. Guénard, B. Blanchard and C. Liu; XTBG (21.919°N, 101.272°E), Rain forest, 05.vi.2013, 10 workers, 550 m, Winkler sifting, B. Guénard, B. Blanchard and C. Liu; “Holy Hills” (21.920°N, 101.239°E), Rain forest, 07.vi.2013, 10 worker, 665m, Winkler sifting, B. Guénard, B. Blanchard and C. Liu; XTBG (21.928°N, 101.256°E), Rain forest, 07.vi.2013, 10 workers, 565 m, Hand collection, B. Guénard, B. Blanchard and C. Liu; Man Sai village (21.860°N, 101.278°E), Rain forest, 12.vi.2013, 1 worker, 680 m, Winkler sifting, B. Guénard, B. Blanchard and C. Liu.

Known from Yunnan (new record), Laos and Thailand (Figure 39C). This new record represents the northern-most record in the distribution of Tetramorium polymorphum.

Tetramorium polymorphum is a member of the Tetramorium walshi species group. Its identification is not easy since the species was not known when Bolton (1976) published his revision of the genus Triglyphothrix (now Tetramorium), in which he provided keys to the Indo-Malayan and Austral-Asian Tetramorium walshi and Tetramorium obesum species groups. However, by combining Bolton’s (1976) work with the recent species description of Yamane and Jaitrong (2011) the identification is relatively straightforward. It is very similar to the closely related and sympatric Tetramorium kheperra Bolton, 1976, and the identification key of Bolton (1976) will lead the user to that species. The recent addition to Bolton’s key provided by Yamane and Jaitrong (2011) clearly separates both species.

Tetramorium polymorphum is a very special member of the genus Tetramorium since it is the only known species that possesses a polymorphic worker caste divisible into distinctive minor, media and major workers (Yamane and Jaitrong 2011). Yamane and Jaitrong (2011) also report that this species is comparatively aggressive and hypothesize that the major worker could have a defensive function. In addition, they emphasize that Tetramorium polymorphum is only found in undisturbed rain forest habitats in Thailand and Laos. Our data from Yunnan supports this since it was predominantly sampled from rain forest.