Tetramorium indicum

A sparse set of disparate data shows a specimen from a forest habitat and sampling from rotten wood, a pitfall trap and low vegetation.

Identification
Like Tetramorium nipponense this species is very close to Tetramorium bicarinatum, but is separable by the characters shown in the key, especially the fact that the long hairs arising dorsally from the frontal carinae are consistently shorter than the maximum diameter of the eye in bicarinatum, and longer in indicum. The eye itself is larger in bicarinatum, its maximum diameter being 0.26-0.29 x HW as opposed to 0.23-0025 x HW in indicum. Colour pattern is also of value in separating the two as in bicarinatum the gaster is always conspicuously darker than the head and alitrunk, whereas in indicum the colour is usually uniform throughout; examples with the gaster slightly darker than the rest of the body are known but they are uncommon.

Without doubt the closest relative of indicum is nipponense and the best characters for separating this pair are those given in the key. The fact that the eyes of nipponense tend to be slightly larger in material examined may not be significant in the long run. In general the ranges of these two species tend to be mutually exclusive, but both forms occur in Bhutan as has been shown by the recent collections made there by Cesare Baroni Urbani.

The range of nipponense appears to be an upland- or mountain one, and the species occurs in a broad belt from Bhutan eastwards across southern and south-eastern China, northern Vietnam, Japan, Okinawa and Taiwan. On the other hand, the distribution of indicum occupies an arc around the eastern end of the Indian Ocean from India to Java, in the forested zones.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Indonesia, Malaysia. Oriental Region: India.

Nomenclature

 *  indicum. Tetramorium guineense var. indica Forel, 1913k: 81 (w.q.) INDONESIA (Sumatra). Raised to species: Bolton, 1977: 98.

Worker
Bolton (1977) - TL 3.7-4.3, HL 0.84-0.96, HW 0.74-0.88, CI 85-92, SL 0.60-0.72, SI 78-85, PW 0.52-0.62, AL 1.00-1.16 (40 measured).

Mandibles finely and usually quite faintly striate, sometimes the striation effaced in places. Clypeus with a notch or impression medially in the anterior margin, the median portion of the clypeus with three strong longitudinal carinae. Frontal carinae long and strong, extending back almost to the occiput. Eyes of moderate size, maximum diameter c. 0.18-0.21, so that the eye is about 0.23-0.25 x HW. Pronotal corners angular in dorsal view. Propodeal spines usually quite short and stout, more rarely elongated, usually approximately straight, elevated but not upcurved along their length nor abruptly and strongly upcurved at their apices. Metapleural lobes triangular, acute and slightly upcurved. Petiole in profile with the anterior face slightly shorter than the posterior so that the anterodorsal angle is on a lower level than the posterodorsal. Rugose sculpture of dorsal head longitudinal to level of posterior margins of eyes, without cross-meshes; behind this a rugoreticulum is present. Dorsal alitrunk reticulate-rugose as are the pedicel segments, although in some the post petiole dorsum tends to be predominantly longitudinally rugose. Gaster usually with vestiges of basal costulae on the first tergite, more rarely unsculptured. All dorsal surfaces of head and body with numerous erect or suberect hairs, the longest of those projecting dorsally from the frontal carinae behind the antennal insertions longer than the maximum diameter of the eye. Colour uniform light brown to mid-brown, rarely with the gaster slightly darker than the alitrunk.

Type Material
Bolton (1977) - Syntype workers, females, Sumatra: Tandjang Sian at and Bah Boelian (Buttel-Reepen) [examined].