Ocymyrmex dekerus

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Ocymyrmex dekerus
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Crematogastrini
Genus: Ocymyrmex
Species: O. dekerus
Binomial name
Ocymyrmex dekerus
Bolton & Marsh, 1989

Ocymyrmex dekerus casent0173608 profile 1.jpg

Ocymyrmex dekerus casent0173608 dorsal 1.jpg

Specimen labels

Nothing is known about the biology of Ocymyrmex dekerus.

Identification

A member of the barbiger group, O. dekerus is closely related to Ocymyrmex robustior and Ocymyrmex barbiger. In barbiger the eyes are smaller than in robustior and dekerus, and generally fail to break the outline of the sides of the head. Also, the petiole node in the former is uniformly strongly sculptured and the cephalic sculpture is strongly developed. O. robustior and dekerus separate on the strength and density of sculpture on the lateral pronotum and on the mesopleuron the oblique costulae are finer and more densely crowded in robustior than in dekerus. Apart from this the clypeal teeth in robustior tend to be longer and more acute than in dekerus, and the occipital margin of robustior is impressed or indented medially, whereas dekerus has this zone transverse or at most extremely feebly concave. (Bolton 1981)

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

Known only from the worker caste.

Worker

Nomenclature

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

  • dekerus. Ocymyrmex dekerus Bolton & Marsh, 1989: 1292 (w.) NAMIBIA.

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 5.8, HL 1.40, HW 1.36, CI 97, SL 1.35, SI 99, PW 0.84, AL 1.80.

Anterior clypeal margin with a median impression. Prominent cuticular flange on anterior clypeal margin narrow and inconspicuous, not a broad lamina. Palp formula 4, 3 (see paratypes). Maximum diameter of eye 0.32, about 0.24 x HW. With the head in full-face view the eyes just intercepting the outline of the sides rather than conspicuously breaking the outline or distinctly failing to reach the outline of the sides. Sides of head in front of eyes parallel, the outline exceptionally weakly concave. Behind the eyes the sides forming an evenly convergent convex broad curve which is confluent with the occipital margin; the latter flattened to very feebly concave medially but not indented. Promesonotum convex, the posterior portion of the mesonotum sloping posteriorly and very shallowly concave to its junction with the propodeum, the latter feebly convex and rounding into the sloping declivity. Metapleural lobe low and rounded in profile, not concealed by the metapleural gland bulla. Node of petiole longer than broad in dorsal view, the postpetiole slightly broader than long and much broader behind than in front. In profile the postpetiolar sternite acutely pointed (see paratypes). Ventrally the postpetiolar sternite with a conspicuous. median longitudinal groove or impression which splits the sclerite into a pair of roughly triangular ventrolateral prominences or tumuli. Gaster in profile with the outline of both the first tergite and first sternite convex behind the articulation with the postpetiole. In dorsal view the base of the gaster not constricted, lacking a neck-like basal area. Dorsum of head very feebly shallowly costulate-rugulose, the sculpture almost effaced in places, .and the ground-sculpture weak to vestigial. Dorsal alitrunk transversely costulate to rugose except for a longitudinal patch centrally on the pronotum and anterior mesonotum. Sides of pro no tum with strongly developed but widely spaced longitudinal costulae, about 12 such costulae present at the pronotal midlength between its basal margin and the level of the base of the mesothoracic spiracle. Remainder of sides of alitrunk obliquely costulate, the components somewhat closer together than on the pronotal sides. Petiole with transverse rugulae ventrally but the sides and dorsum predominantly reticulate to shagreenate. Standing hairs present on all dorsal surfaces of head and body. Colour brown, the head and gaster with a dull yellowish to dull orange tint, the alitrunk with a dull reddish tint.

Paratypes. TL 5.8-6.0, HL 1.40-1.54, HW 1.36-1.48, CI 96-99, SL 1.35-1.42, SI 95-99, PW 0.84-0.90, AL 1.80-1.88 (5 measured).

As holotype but maximum diameter of eye 0.32-0.34 (about 0.22-0.24 x HW). Sides of head in front of eyes vary from very feebly concave to more or less straight in full-face view. One worker has the left maxillary palp 3-segmented, the right 4-segmented; the reduction of the left palp is due to the fusion of the two small apical palpomeres. Shape of the postpetiolar sternite in profile is variable. In the holotype it is acutely pointed on each side, but the para types show variation from this shape to bluntly rounded. Cephalic sculpture is somewhat stronger in some para types than in the holotype, the costulate-rugulose component being more obviously developed. Colour varies from that described above to a more or less uniform light to medium brown, often with a yellowish tint to the gaster.

Type Material

Holotype worker, Namibia ( = South West Africa): 9 mi. NW of Grunau, 1150 m 4.v. 1958 (E. S. Ross and R. E. Leech) (California Academy of Sciences). Paratypes, 5 workers with same data as holotype (CASC, The Natural History Museum).

References