Myrmoteras iriodum

Nests are small, typically less than 20 workers, and have been found under rocks in forest habitat.

Identification
Moffett (1985) - Head smooth, lacking sculpture. Distinguished from Myrmoteras mjoebergi by its relatively long mandibles (ML > 1.30), relatively strong iridescence, five-segmented maxillary palps, and by the dense pilosity.

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

Biology
Ito et al. (2017) were able to collect whole colonies. Nests were typically found under stones in the forest floor and were collected in Ulu Gombak (3°19’N; 101°45’E; 250 m a.s.l.), Selangor, Peninsular Malaysia between 1992 and 2016. Colonies are monogynous and queens found colonies non-claustrally. Colony size is very small, workers per colony = 8.2 + 7.1 (+ SD), N = 11, maximum 22. Ovariole number for queens is small with a total of just four per individual.

Reproductive queens and larvae feed on liquid food from workers and solid prey items. Second, the condition of immatures of M. iriodum in the nest chamber seems different from other species in the genus. Myrmoteras toro and Myrmoteras jaitrongi make clusters of eggs and small larvae, whereas M. iriodum never makes such clusters inside their nest. Workers of M. toro often held a larva or pupa by gently gripping them between the mandibles or immobilized them with their forelegs (Moffett 1986). Such behavior was rare in M. iriodum, as larvae and pupae usually laid on the nest floor. Foraging and contact with prey: Workers kept their mandibles fully opened (ca. 280 degrees) most of the time they spent in the foraging arena. When they encountered prey animals, they slowly approached them. If prey animals moved fast, the workers chased the prey a bit but usually gave up. When they could be sufficiently close to have the prey within reach of the tips of the trigger hairs, they strike the prey by very quickly snapping the elongate mandibles. Closing the mandibles was powerful enough to kill the soft body arthropods they hunt for. When hunting for prey, workers never used formic acid, although they do possess a functional venom gland as is typical for formicine ants (Billen et al., 2015). When offered small (body length ca. 0.4 mm) and large springtails (ca. 1.3 mm) simultaneously, the ants preferred to attack the smaller prey. Beside springtails, they also attack young termite nymphs and small cricket nymphs. Foraging workers and virgin queens licked diluted sugar water in the foraging arena.

Prey feeding: Foraging ants brought prey items back to the nest chamber, and began to masticate prey by holding it between the tips of the mandibles. During prey mastication, workers and queens crossed the mandibles repeatedly, and sometimes adjusted the position of prey with their forelegs. They often fed on the masticated prey by bringing it with their forelegs to the mouthparts. After the foragers had fed on the prey they retrieved, they passed the masticated prey on to the larvae, fellow workers or both virgin and reproductive queens. When prey size was large, a few ants cooperatively masticated it. The queens and workers often fed on the masticated prey that was placed on the larval mouthparts. Inside the nest chamber, stomodeal trophallaxis among female individuals was often observed. Mated queens frequently received trophallaxis from workers, however, feeding directly on prey brought by workers was also observed.

Brood care: Larvae and pupae were scattered on the nest floor. No clusters of eggs and microlarvae were organized. The reproductive queen rarely showed brood care, except for egg care just after oviposition. Workers and dealated virgin queens often inserted their mandibles between the nest floor and larvae, opening the mandibles ca. 30 degrees and then quickly closed them, this behavior was repeated a few times. The function of this behavior, however, was unclear.

Oviposition: Egg-laying by the queens was observed only once. The queen bent her abdomen forward underneath the thorax and extruded an egg from the tip of the abdomen. The egg was picked up by the queen herself with the mandibles.

Nomenclature

 *  iriodum. Myrmoteras (Myrmoteras) iriodum Moffett, 1985b: 24, figs. 13, 17 (w.q.) BORNEO.

Worker
Holotype (HW 1.20) and five paratypes: TL 6.4 to 6.8, HW 1.14 to 1.20, HL 1.17 to 1.22 (CI 97 to 99), ML 1.68 to 1.74 (MI 142 to 145), SL 1.36 to 1.40 (SI 115 to 120), EL 0.72 to 0.76, HFL 1.49 to 1.56 (TWI 17 to 19), WL 1.80 to 1.85 mm.

Only a trace of the frontal sulcus is visible. Trigger hairs unusually short, projecting only ca. 0.45 to 0.50% of distance to mandible tips (ca. 75 to 90% in randomly selected individuals from other species except for two lof four measured] Myrmoteras binghamii specimens with measurements of ca. 60%). Palpal segmentation 5,3 (three specimens examined). Mandibles relatively longer than in other species of the subgenus, and with 11 to 13 teeth (usually 12) and 2 to 3 preapical denticles (usually two); apical denticle pair with distal denticle unusually massive, stout. Distal portion of mandible shafts somewhat less strongly bent downward than in Myrmoteras mjoebergi.

Pronotum low and evenly convex; propodeum slightly flattened above. Metanotal groove conspicuously impressed. Node of petiole distinctive, similar to M. mjoebergi, but taller and more massive, with anterior face a long vertical drop; summit narrow (relative to base) and rounded; posterior face sloping, slightly convex to straight. Summit of node evenly rounded when viewed from behind. Ventral margin of petiole feebly convex to virtually straight beneath node.

Head and trunk only very feebly lustrous, but more strongly iridescent than in other species, and with other parts of the body more feebly iridescent. Head, pronotum and propodeum smooth (very slight surface irregularities could possibly represent traces of a granulate sculpture); mesothorax very feebly and irregularly rugose dorsad, where rugae are largely transverse. Laterally mesothorax irregularly sculptured with narrow rugae, and in some cases with a narrow ruga extending forward to pronotum from base of metathoracic tubercle, much as in most species of the donisthorpei and bakeri groups of Myrmoteras. Pilosity dense to very dense, with 33 to 42 hairs breaking dorsal margin of trunk in profile. Hairs short, rising 0.08 mm on head and 0.10 mm on trunk and gaster. Two or three hairs on or near each metathoracic tubercle; node of petiole with 8 to 14 hairs. Orange with slight reddish tinge, virtually uniform except trunk slightly darker reddish orange and gaster orange yellow.

Queen
Paratype: TL 7.0, HW 1.23, HL 1.24 (CI 101), ML 1.68 (MT 135), SL 1.38 (SI 110), EL 0.77, HFL 1.54 (TWI 18), WL 1.90 mm. Trunk smooth, although possibly with traces of a granulate sculpture; propodeum feebly and irregularly transversely rugose dorsad. Head very feebly longitudinally rugose between bases of antennae.

Type Material
Holotype. Worker deposited in MCZ from Borneo: SE Kalimantan: 17 to 46 km W. Batulitjin, 28 June to 2 July 1972, lowl. rainfor., hollow stick in litter, B-18, (W. L. Brown). Paratypes. Six workers with same date and collection number, and one dealate queen with same data but labelled "abandoned earthen termite nest".

Etymology
Name a noun in apposition from Gr. iriodes, referring to the relatively strong iridescence on the head and trunk.