Ocymyrmex zekhem

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

Ocymyrmex zekhem castype13685 profile 1.jpg

Ocymyrmex zekhem castype13685 dorsal 1.jpg

Specimen labels

A Namibian series collected by Alan Marsh at Samanab River (Skeleton Coast), Swakopmund, and two workers from Hunkab Springs, belong to this species, which was previously known only from the holotype.

Identification

A member of the velox group. Bolton and Marsh (1989) - O. zekhem is closely related to Ocymyrmex velox but differs in being generally darker in colour, having long standing hairs on the first gastral tergite which equal the length of the erect hairs on the propodeum, and by having longer scapes (SI > 110) than are seen in velox (SI < 110). The samples of zekhem now available indicate that the intensity of cephalic sculpture is slightly variable, as specimens with more conspicuous dorsal cephalic costulae than others are fairly frequent. The occipital region varies from very feebly striolate to virtually smooth. Colour in zekhem varies from having the head very dark dull red to reddish or brownish black. The alitrunk is always glossy jet black. The gaster is blackish brown but the petiole and postpetiole may have a reddish tint. Currently the known range of dimensions in zekhem are TL 8.0-9.5, HL 2.06-2.20, HW 1.90-2.04, CI 91-93, SL 2.20-2.28, SI 111-116, PW 1.22-1.40, AL 2.50-2.70 (10 measured).

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Afrotropical Region: Namibia (type locality), South Africa.

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.

  • zekhem. Ocymyrmex zekhem Bolton, 1981b: 281 (w.) NAMIBIA. Bolton & Marsh, 1989: 1278 (q.). See also: Bolton & Marsh, 1989: 1306.

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 8.4, HL 2.06, HW 1.90, CI 92, SL 2.20, SI 116, PW 1.40, AL 2.50.

Anterior clypeal margin entire, without trace of a median notch or impression. Maximum diameter of eye 0.40, about 0.21 x HW, the eyes only just failing to break the outline of the sides in full-face view. Sides of head in front of eyes straight, diverging anteriorly; behind the eyes the sides rounding broadly and evenly into the occipital margin, the latter very shallowly impressed medially in full-face view. Antennal scapes the longest yet known in the genus (see SI, above). With the alitrunk in profile the promesonotum low, evenly shallowly convex. Posterior part of mesonotum and anterior part of propodeum sloping gently downwards posteriorly, the posterior half of the propodeal dorsum levelling off for a short distance before rounding smoothly into the gently convex declivity. Metapleural lobes low and narrow, rounded and only slightly projecting, but not at all concealed by the metapleural gland bulla in absolute profile. Petiole in profile with ventral surface of peduncle shallowly sinuous but without a developed process. Dorsal surface of peduncle also irregular and passing through a blunt angle about one-third the way from the base. Petiole node evenly rounded and dome-like in profile; long and narrow in dorsal view, longer than broad and no broader than the posterior peduncle, the sides of the node scarcely convex. Postpetiole in dorsal view broader than long. Base of first gastral tergite no wider than the postpetiole in dorsal view but not forming a narrow neck; instead the sides of the tergite diverge quickly and evenly from the base. Dorsum of head with sculpture almost effaced, the surface between the eyes with faint narrow longitudinal costulae which are quite close-packed and almost effaced in places. Occipitally the costulae present are even weaker than between the eyes and are transverse. Ground-sculpture between the narrow costulae everywhere vestigial or absent, the surface shining and mostly smooth. Dorsum of pronotum transversely arched-rugose, centrally with an area of longitudinal rugosity; everywhere else the alitrunk transversely rugose. Sides of alitrunk more strongly sculptured than dorsum, the rugae no denser but more sharply defined and more strongly developed. Petiole, postpetiole and gaster unsculptured except for a faint superficial reticular pattern. All dorsal surfaces of head and body with numerous standing hairs. Basal half of first gastral tergite with a number of conspicuous long hairs which are as long as those on the dorsal alitrunk. Head very dark dull red, alitrunk glossy jet black, remainder of body blackish brown but the pedicel segments with a reddish tint. Legs and antennae dark dull red to reddish dark brown, approximately the same colour as the sides of the head.

Type Material

Holotype worker, South West Africa: Tsisab Cyn., Brandberg Mts, 550 m, 11.v.1958 (E. S. Ross & R. E. Leech) (California Academy of Sciences).

References