Tetramorium difficile

The holotype was collected from a forest litter sample.

Identification
A member of the Tetramorium tonganum-species group.

Bolton (1977) - T. difficile shows affinity with Tetramorium tonganum but is smaller than that species and has relatively shorter antennal scapes. Also, the pronotal corners in tonganum are very broadly rounded, whilst those of difficile are more angular (though not sharply so).

A series from Bhutan: Phuntsholing, 1972,2/400 m (Baroni Urbani) in NM, Basle, compares well with the type-series but the individuals are somewhat darker in colour (mid-brown) and in some the propodeal spines are slightly but definitely longer than the metapleural lobes. The metapleural lobes themselves are somewhat more acute than in the types. Despite these (relatively minor) differences I feel sure that this series from Bhutan represents part of the normal variation of difficile.

Distribution based on Regional Taxon Lists
Oriental Region: Nepal. Palaearctic Region: China.

Nomenclature

 *  difficile. Tetramorium difficile Bolton, 1977: 126 (w.) NEPAL.

Worker
Holotype. TL 2.4, HL 0.56, HW 0.52, CI 93, SL 0.40, SI 77, PW 0.38, AL 0.64.

Mandibles striate; anterior clypeal margin entire and the median portion with a narrow anterior flange or apron. Frontal carinae well developed, reaching back well beyond the level of the eyes and forming the upper borders of the shallow but quite distinct antennal scrobes. Maximum diameter of eye c. 0.12, about 0.23 x HW. Propodeal spines short and dentiform, slightly shorter than the short, bluntly triangular metapleural lobes. Petiole in profile with a slightly downcurved anterior peduncle, the node itself has rounded anterodorsal and posterodorsal angles and the tergal portion is slightly higher than the length of the dorsum. Postpetiole in profile evenly convex. In dorsal view the petiole node is slightly broader than long and the postpetiole is only slightly broader than the petiole. Dorsum of head weakly longitudinally rugulose, with some feeble reticulation occipitally. Dorsal alitrunk finely reticulate-rugulose, the petiole node with faint traces of rugulation dorsally. Post petiole and gaster unsculptured and shining. All dorsal surfaces of head and body with numerous fine hairs of varying length but the scapes and dorsal (outer) surfaces of the hind tibiae only with short, decumbent or appressed pubescence, without longer hairs. Colour uniform yellowish brown.

Paratype. As holotype, TL 2.3, HL 0.54, HW 0.50, CI 93, SL 0.38, SI 76, PW 0.36, AL 0.62. Maximum diameter of eye 0.12, about 0.24 x HW.

Type Material
Holotype worker, NEPAL: Tamur R., Dobhan, l.ii.l962, forest litter (K. Hyatt). Paratype. 1 worker with same data as holotype.