Ocymyrmex ankhu

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Ocymyrmex ankhu
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Crematogastrini
Genus: Ocymyrmex
Species: O. ankhu
Binomial name
Ocymyrmex ankhu
Bolton, 1981

Ocymyrmex ankhu casent0173610 profile 1.jpg

Ocymyrmex ankhu casent0173610 dorsal 1.jpg

Specimen Label

Nothing is known about the biology of Ocymyrmex ankhu.

Identification

Bolton (1981) - A member of the velox group. O. ankhu is closest related to Ocymyrmex velox and shares most of its diagnostic characters. However, ankhu is more or less uniformly coloured and has the body pilosity reddish brown. In velox the body is conspicuously tricoloured and the hairs are usually white.

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Afrotropical Region: Angola (type locality).

Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Biology

Little is known about the biology of this species but a few species of Ocymyrmex have been studied in some detail. From this we can form some ideas about the biology of the genus as a whole. The following is summarized from Bolton and Marsh (1989). More details can also be found on the Ocymyrmex genus page.

Arnold (1916) observed that Ocymyrmex species with which he was acquainted nested in the ground in hot arid areas. The nests themselves went very deep into the ground, usually in loose sandy soil, and had a crater-like entrance. The ants used their well-developed psammophores to carry soil particles excavated from the nests. Recently both Marsh and Robertson (pers. comm.) have observed that workers of Ocymyrmex fortior close the nest entrance with small stones during periods of nest inactivity. Also, in Zimbabwe, fortior workers have been seen adding small stones to the crater-like nest entrance that were picked up from the ground some distance away from the nest. Species are now known which nest in very rocky soil and the nests may extend through the bedrock itself, necessitating the use of a large crowbar to expose the nest-chambers (H. Robertson, pers. comm.). Careful excavations of nests in well-structured sandy soil by one of us (Marsh) have revealed a simple nest structure. For example, nests of foreli typically have one entrance that opens into a vertical tunnel which terminates in a broad chamber at a depth of about 30 cm. Other brood and food chambers branch off from the tunnel at various intermediate levels. In most nest excavations the ergatoid queen was discovered near the bottom of the nest. In very unstructured loose sand, such as in the dry river beds of the Namib Desert, the tunnels and chambers of Ocymyrmex nests followed the root systems of shrubs and trees, and the major tunnel was therefore not necessarily vertical. Colonies of Ocymyrmex range in size from 200 to 1000 individuals (Marsh, 1987).

Other general aspects of their biology include workers that move rapidly, erratically, and are often active during the hottest part of the day. Specifics of their diet seem to vary by species but can include seeds and insects. For most species where queens are known they are worker-like ergatiod forms that are nonetheless clearly a morphologically distinct caste, as opposed to many intercaste ergatiods known from other genera that are intermediate between workers and more robust queens. Males of Ocymyrmex are often collected at lights but males associated with conspecific workers and females have rarely been collected.

Castes

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • ankhu. Ocymyrmex ankhu Bolton, 1981b: 265 (w.q.) ANGOLA.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

Worker

Holotype. TL 10.2, HL 2.34, HW 2.35, CI 100, SL 2.30, SI 98, PW 1.50, AL 2.96.

Anterior clypeal margin entire, without a strong median notch flanked by a pair of teeth but only with a tiny erosion of the apron where the weak median clypeal carina runs into it. Maximum diameter of eye 0.42, about 0.18 x HW, the eyes conspicuously failing to break the outline of the sides of the head in full-face view. Sides of head extremely weakly divergent anteriorly, rounding broadly and evenly into the occipital margin which is shallowly convex on each side of a median indentation. Alitrunk in profile with the promesonotum low and very shallowly convex, almost flat dorsally but with the posterior half of the mesonotum sloping more steeply downwards. Propodeal dorsum almost flat, with an exceedingly shallow depression in the surface just in front of the level of the spiracle. Posteriorly the propodeal dorsum rounding broadly and evenly into the shallowly convex declivity. Metapleural lobes low and truncated posteriorly. Petiole in profile large, broadly dome-like and rounded, the anterior peduncle without trace of a ventral process. In dorsal view the petiole node very slightly longer than broad, rounded and with evenly convex sides. Postpetiole in dorsal view broader than long. Base of first gastral tergite no broader than the postpetiole but not constricted to a narrow neck; instead the sides diverge quickly and evenly from the base. Dorsum of head between eyes with faint superficial vestiges of fine and quite dense rugular or costulate sculpture which in places is almost effaced. Ground sculpture absent except for the faintest remnants of a minute superficial reticulation, the surface mostly smooth and glossy and the scattered hair pits quite clearly visible. Occipital region of head mostly smooth but a narrow strip in front of this with feeble transverse sculpture. Pronotal dorsum mostly smooth, with marginal remnants of fine arched rugulae and vestiges of the longitudinally sculptured area between the mesothoracic spiracles just visible. Remainder of dorsal alitrunk very finely and feebly transversely rugulose, with a tendency for the rugulae to fade out centrally. Sides of alitrunk more strongly and more sharply rugulose or costulate, weaker on the pronotal sides than elsewhere. Petiole, postpetiole and gaster unsculptured except for a fine superficial reticulation. Dorsal surfaces of head, alitrunk, petiole and postpetiole with numerous strong reddish brown hairs. Basal half of first gastral tergite hairless but more apically the segment with 1-2 very short, inconspicuous hairs. Colour a uniform rich orange-brown, the gaster very slightly lighter in shade than the head and alitrunk.

Paratypes. TL 9.7-10.2, HL 2.26-2.34, HW 2.22-2.34, CI 97-101, SL 2.22-2.34, SI 95-102, PW 1.40-1.48, AL 2.84-2.92 (7 measured). Maximum diameter of eye 0.42-0.44, about 0.18-0.19 x HW. As holotype.

Type Material

Holotype worker, Angola: 5 miles [8 km] E. of Vila Arriaga, 1000 m, 21.v.1958 (E. S. Ross & R. E. Leech) (California Academy of Sciences). Paratypes. 7 workers and I female with same data as holotype (CASC, The Natural History Museum, Museum of Comparative Zoology).

References