Acanthomyrmex ferox

A colony of nearly fifty workers was collected in southern Borneo nesting in leaf litter in disturbed primary rainforest (Moffett, 1985).

Identification
Moffett (1986) - Petiolar node of both worker castes with long, dorsally directed lateral spines, and postpetiole with a high, rounded node. Minor worker with conspicuous alveolate sculpture.

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

Biology
Soldiers have specialized morphological traits that allow two distinct functions: (1) trophic eggs are produced in ovaries (6 ovarioles) that are the same as in queens (Gobin & Ito 2000); (2) mandibles are modified in shape to crush fig seeds, just as in queens. A. ferox colonies (n=49) have 25±11 workers and 2.6±1.5 soldiers (Gobin & Ito 2000).

Ito, Gobin and Hashim (2017) - Foragers can be found on the forest floor and on low vegetation, typically in gaps and forest edges where sunlight reaches the ground (Ulu Gombak field station, Peninsular Malaysia). Nests occur in small dead twigs and accumulated dead leaves. Fig seeds were collected by the workers with field observations revealing the source of these seeds were from bird droppings. In the laboratory workers would also harvest fig seeds when offered, suggesting the seeds would be collected if found independent of bird feces.

Nomenclature

 *  ferox. Acanthomyrmex ferox Emery, 1893f: 245 (footnote), pl. 6, fig. 11 (w.) WEST MALAYSIA. Moffett, 1986c: 72 (s.q.m.). Senior synonym of dyak: Moffett, 1986c: 70. See also: Moffett, 1985a: 165.
 * dyak. Acanthomyrmex dyak Wheeler, W.M. 1919e: 86 (s.w.) BORNEO. Junior synonym of ferox: Moffett, 1986c: 70.

Worker
Moffett (1986) - Minor. The two syntypes measure HW 1.06 to 1.12, HL 1.00 to 1.05 (CI 106 to 107), ML 0.83 (MI 83), SL 1.26 to 1.28 (SI 114 to 120), EL 0.20 to 0.21, HFL 1.38 to 1.39 (FLI 132 to 139; FWI 19 to 20) mm. Head shape as in Acanthomyrmex notabilis, i.e., virtually rounded across posterior margin in full-face view, although slightly flattened or with a trace of a concavity mesad. Maximum head width virtually the same above and below eyes. Cephalic sculpture best described as areolate or alveolate rather than foveate, as the foveae have angular walls and are separated by thin partitions; longer hairs on dorsum of head extend 0.15 mm. Clypeal index 91 to 93. Feeble lobe present on each side of medial clypeal hair; lateral clypeal hairs not in a well-defined fovea. Clypeus virtually smooth, and without two longitudinal rugae present to demarcate a medial clypeal region. Mandibles lacking a ventral tooth.

Spines on trunk virtually straight (propodeal spines with a slight curvature caudad); pronotal spines hairy, and consistently longer than those on propodeum. Pronotal angle drawn out into a feeble tooth (Fig. 24: indistinct or absent in some other specimens and on one side of a syntype). Propodeal declivity bordered on each side by a single rugum, as described for Acanthomyrmex crassispina.

Node of petiole as in figure, PWI wide (120 and 138). Anterior peduncle of petiole relatively short and deep, and with lateral and sublateral hairs; subpetiolar declivity present. Postpetiole smooth (although with feeble foveae on node); with convex lateral margins in dorsal view (rather than rectangular), and almost as long as it is wide. Postpetiole having a distinctive high, rounded node with scattered hairs. Dorsal surface of gaster hairy, but with hair density sparser than in most other luciolae group species. Femora hairy, and with ventral surfaces only feebly concave. Orange yellow, with legs and gaster lighter and with more yellow.

Major. Three Sarawak majors from two series (single major from Peninsular Malaysia very similar): HW 2.42 to 2.58, HL 2.45 to 2.48 (CI 99 to 104), SL 1.20 to 1.25 (SI 47 to 52), EL 0.26 to 0.28, HFL 1.54 to 1.56 (FLI 63 to 68; FWI 20) mm. Frons costate up to level of scrobes (and laterally up to level of eyes); vertex relatively densely foveate (comparison of specimens suggests the foveae become denser and more deeply impressed in progressively smaller majors). No distinct cephalic hollow. No darkly pigmented streak dorsad on head; wide medial sulcus conspicuous, low on face. Forward margin of clypeus with a medial projection. Propodeal spines long, as in minors but thicker at bases. Pronotal angle lacking the feeble tooth characteristic of the minor caste.

Queen
Moffett (1986) - Three queens (from Peninsular Malaysia, Sarawak, and Kalimantan) measure HW 1.86 to 2.30, HL 1.54 to 1.83 (CI 121 to 126), ML 1.08 to 1.20 (MI 65 to 70), SL 1.10 to 1.21 (SI 52 to 59), EL 0.28 to 0.33, HFL 1.53 to 1.68 (FLI 92 to 97; FWI 20 to 21) mm. Head broad, with lateral margins divergent, and widest near vertex; posterior margin slightly concave mesad. Head with narrow, wavy longitudinal rugae, forming foveae behind level of ocelli and laterally; foveae feeble beneath head. Medial sulcus narrow but conspicuous beneath ocelli. Scrobes prominent, as in majors. Clypeus smooth, with projecting medial lobe as in major. Trunk irregularly rugose laterally (especially on propodeum), smoothest on anepisternum and pronotum. Dorsum with numerous foveae, and with rugae extending forward onto mesonotum from its posterior border. Posterior margin of scutellum with short, stout horns laterally. Propodeal spines short and stout, projecting caudad. Anterior peduncle of petiole short and deep; node of petiole broad, with lateral spines greatly shortened relative to worker castes. Postpetiole narrower than in workers, more than 50% wider than long in dorsal view. Petiole and postpetiole with more pilosity than in workers, but otherwise pilosity similar to workers.

Male
Moffett (1986) - Measurements of five specimens from southern Kalimantan (male from Peninsular Malaysia very similar): HW 0.93 to 1.03, HL 0.76 to 0.82 (CI 123 to 128), ML 0.46 to 0.51 (Ml 56 to 64), SL 0.56 to 0.63 (SI 57 to 61), EL 0.30 to 0.32 mm. Head broad, widest immediately above eyes; vertex broad, posterior margin of head feebly concave. Head sculptured as in minor workers but less regular and much more feeble; pilosity long, rising 0.25 mm dorsally. Clypeus irregularly longitudinally rugose, forward margin lacks projecting lobes. Trunk as described for queen, but propodeal spines lacking; feebly and irregularly rugose dorsally with only traces of foveate sculpture. Both petiole and postpetiole with low, rounded nodes; postpetiole somewhat longer than wide in dorsal view. Jet black, with legs and gaster dark brown and mandibles dark yellowish orange.

Height of pilosity variable, with the longer hairs dorsally on the head extending about 0.15 mm in the syntypes and in the specimens from Kalimantan, Pahang (Malaysia) and the Gombak (Malaysia) specimen collected by Imai, but shorter (0.08 to 0.10 mm) in other series. Most of the workers with shorter cephalic pilosity have relatively sparse (and very short) pilosity on their gasters, and some also lack pilosity on their pronotal spines.

The traces of very fine rugulose sculpture present on the lateral surfaces of the mandibles of most Acanthomyrmex minor workers is generally absent in Acanthomyrmex ferox, although this microsculpture can be discerned in the types. Petiolar node with spine length and curvature somewhat variable, PWI 105 to 143. Postpetiole of all major workers and some minors (i.e., those from Lampongs and Sarawak) with conspicuous foveae on node, as in individual in figure. Femora sometimes more concave beneath than in syntypes, particularly in the Bolton specimens from Sarawak and the Perak (Malaysia) worker. Color in most specimens darker than in syntypes, reddish orange.

Acanthomyrmex dyak minor syntypes (HW 1.00 and 1.04 mm) very similar to other A. ferox material; major syntype small (HW 2.28 mm), but not as small as the Sabah major (HW 1.98 mm); otherwise very similar to the Sarawak specimens described above. Tooth lacking at pronotal angle in both castes. Femora flattened or at most feebly concave beneath.

Type Material
Moffett (1986) - Peninsular Malaysia: Perak, two minor workers (M. M. Staudinger, and  [examined]).