Strumigenys exilirhina

Known from disturbed habitats, e.g., rubber plantations, and natural habitats, e.g., rainforest. Samples have been collected under moss and in litter samples. This is one of the most common species of Strumigenys in Hong Kong. It has been collected in a variety of habitats including disturbed urban forests, tree plantations (Lophostemon confertus Wilson & Waterh.), shrubland, secondary forest, and Feng Shui woods. The known elevation range in Hong Kong for this species is from 1 to 407 m (Tang et al., 2019).

Identification
Bolton (2000) - A member of the feae complex in the Strumigenys mayri-group. Series from Thailand tend to have the preapical tooth slightly smaller and somewhat closer to the apicodorsal tooth that does material from elsewhere. At present I am not able to decide if this is significant at species rank or is geographical variation within a single species; suffice to say that apart from this small difference all samples are remarkably similar.

S. exilirhina is closest related to Strumigenys stenorhina of China and Japan but tends to be smaller and have slightly shorter mandibles and scapes (compare measurements). Apart from the key characters the upper scrobe margins of exilirhina are distinctly convex from just in front of the level of the eyes to the scrobe apex; in stenorhina the upper scrobe margins are almost straight in this area and distinctly more straight-divergent posteriorly. Both of these species separate from Strumigenys rallarhina as the latter has a long spiniform preapical tooth on the mandible, whereas in both exilirhina and stenorhina the preapical tooth is short and triangular. S. exilirhina and stenorhina together are closely related to Strumigenys kraepelini and Strumigenys barylonga but the last two tend to be larger and are decidedly more slender, attenuated species with long scapes and very narrow heads.

Distribution based on Regional Taxon Lists
Oriental Region: Bhutan, India, Nepal, Thailand. Palaearctic Region: China, Japan.

Biology
Using Malaise traps at various locations in Hong Kong, Tang et al. (2019) collected female alates in sampling conducted from mid-May to mid-June.

Nomenclature

 *  exilirhina. Strumigenys exilirhina Bolton, 2000: 881 (w.q.) NEPAL.

Worker
Holotype. TL 2.4, HL 0.66, HW 0.44, CI 67, ML 0.29, MI 44, SL 0.41, SI 93, PW 0.26, AL 0.64. Characters of the feae-complex. Preapical tooth elongate-triangular and slightly recurved, slightly shorter than width of mandible at point where tooth arises. Outer margin of mandible in full-face view shallowly convex from close to base to level of preapical tooth; inner margin between same points shallowly concave to almost straight. Upper scrobe margin with two freely laterally projecting long flagellate hairs, the posterior one in apicoscrobal position. Cephalic dorsum with 4-6 erect subflagellate or looped hairs along the occipital margin, a similar but shorter pair at level of highest point of vertex. Preocular notch absent but ventrolateral margin of head narrowed immediately in front of eye. Maximum diameter of eye varying from slightly greater to slightly less than the maximum width of the scape; 3-4 ommatidia across the greatest diameter. Pronotal humeral hair flagellate; pronotal dorsum finely reticulate-punctate and without erect hairs; mesonotum with 2 pairs of erect flagellate hairs. Dorsal surfaces of waist segments and first gastral tergite with flagellate hairs. Pleurae and side of propodeum smooth. A long fine erect flagellate hair present on the dorsal (outer) surface of the hind basitarsus and another on the hind tibia; similar pilosity present on the other legs. Petiole in profile with anterior face of node slightly shorter than length of dorsum, or the two subequal. Disc of postpetiole smooth. Basigastral costulae shorter than disc of postpetiole.

Paratypes. TL 2.2-2.4, HL 0.62-0.67, HW 0.42-0.45, CI 64-68, ML 0.27-0.29, MI 42-45, SL 0.40-0.43, SI 93-96, PW 0.25-0.26, AL 0.60-0.64 (8 measured).

Dimensions of non-paratypic workers. TL 2.3-2.7, HL 0.63-0.78, HW 0.42-0.51, CI 65-68, ML 0.27-0.33, MI 42-46, SL 0.38-0.48, SI 88-96 (12 measured).

Type Material
Holotype worker, Nepal: Sanghu, 3.x.1961, in moss on rock (K. H. Hyatt). Paratypes. 19 workers and 2 queens with same data as holotype (BMNH,, , ).