Ocymyrmex sobek

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

Ocymyrmex sobek casent0235945 p 1 high.jpg

Ocymyrmex sobek casent0235945 d 1 high.jpg

Specimen Labels

Nothing is known about the biology of Ocymyrmex sobek.

Identification

A member of the weitzeckeri group. This strongly sculptured and conspicuously coloured species is closest related to Ocymyrmex foreli. Among the species with a clypeal impression and a distinctly constricted first gastral segment only two, sobek and foreli, have the petiole much enlarged and very strongly sculptured. The two are best separated on their colour but it is also notable that the rugae on the petiole node are narrower and more sharply defined in foreli than in sobek, where they tend to be blunted and much less regular on the dorsum. (Bolton 1981)

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Afrotropical Region: Botswana (type locality), South Africa, Zimbabwe.


Distribution based on AntMaps

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Distribution based on AntWeb specimens

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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

Worker

Nomenclature

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

  • sobek. Ocymyrmex sobek Bolton, 1981b: 277, fig. 20 (w.q.) BOTSWANA.

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 7.8, HL 1.90, HW 1.82, CI 96, SL 1.70, SI 93, PW 1.18, AL 2.44.

Anterior clypeal margin with a conspicuous median semicircular impression which is flanked by a pair of small teeth. Occipital margin in full-face view feebly indented medially, the margin continuous with the sides through a broad, shallow curve. Maximum diameter of eye 0.40, about 0.22 x HW. Promesonotum in profile evenly convex, the dorsum of the propodeum rounding broadly and evenly into the declivity. Metapleural lobes small, subtriangular in shape, but plainly visible in profile and not concealed by the bulge of the metapleural glands. Ventral surface of peduncle of petiole without a projecting process, the node strongly swollen and conspicuous. In profile the large node with a developed posterodorsal angle, not rounded as is usual in the genus. In dorsal view the petiole node massive, almost as large as the post petiole ; the latter also somewhat swollen, about as high as long in profile and broader than long in dorsal view. Base of first gastral tergite constricted, in dorsal view forming a neck behind the postpetiole which is narrower than the maximum width of the postpetiole itself. Dorsum of head finely and densely costulate to rugulose, the sculpture most regular on the central strip of the dorsum. On each side of this central strip the rugulae more wavy and irregular, and tending to diverge posteriorly towards the occipital corners, arching round above the eyes. Spaces between the rugulae with fine dense punctulate ground sculpture. Anterior portion of pronotum with arched-transverse rugae, behind this with an area where the rugae are almost longitudinal, very slightly oblique, running back between the mesothoracic spiracles; remainder of dorsum and also propodeal declivity coarsely transversely rugose. Sides of alitrunk coarsely rugose. Node of petiole coarsely rugose, the rugae continuous, running transversely on the ventral surface, up the sides of the node and across the dorsum; on the dorsum less regular than elsewhere. Anterior face of node and dorsum of peduncle in front of node also transversely rugose. Postpetiole unsculptured except for fine superficial shagreening. Dorsal surfaces of head, alitrunk and pedicel segments with numerous strong hairs. First gastral tergite with hairs much shorter and sparser than elsewhere. Alitrunk dull reddish black (appearing black to the naked eye); gaster dull yellowish red, much lighter than the alitrunk and contrasting strongly with it; head a dull red intermediate in shade between gaster and alitrunk so that the ant appears tricoloured to the naked eye.

Paratypes. TL 7.6-8.0, HL 1.70-1.90, HW 1.64-1.88, CI 93-100, SL 1.56-1.74, SI 92-99, PW 1.08-1.20, AL 2.20-2.44 (11 measured). Maximum diameter of eye 0.36-0.40, about 0.22-0.24 x HW. Answering description of holotype but some with the posterodorsal angle of the petiole more rounded and the pronotal sculpture showing the usual variation, with differences in extent and direction of the longitudinal component. In most the longitudinal rugae are antero-posteriorly straight, but in some (as in the holotype) they are oblique and in a few decidedly transverse. Sculpture pattern on the dorsum of the head is usually as described above but in a few the rugulae run straight back everywhere, not diverging towards the occipital corners, and in one the rugulae between the eye and the central strip of the head are more or less all transverse.

Size range in the non-paratypic material is TL 7.6-8.8, HL 1.80-2.00, HW 1.70-1.96, CI 93-98, SL 1.64-1.80, SI 91-98, PW 1.12-1.28, AL 2.24-2.52 (15 measured). Measurements of eyes all fall within the range of the paratype-series.

Type Material

Holotype worker, Botswana: Smiti, no. 16, mopane woodland, 11.ix.1975 (A. Russell-Smith) (The Natural History Museum). Paratypes. 11 workers with same data as holotype (BMNH, Museum of Comparative Zoology, Naturhistorisches Museum, Basel, Musee d'Histoire Naturelle Genève, NM, Bulawayo).

References