Ocymyrmex velox

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Ocymyrmex velox
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Crematogastrini
Genus: Ocymyrmex
Species: O. velox
Binomial name
Ocymyrmex velox
Santschi, 1932

Ocymyrmex velox casent0217900 p 1 high.jpg

Ocymyrmex velox casent0217900 d 1 high.jpg

Specimen Labels

Marsh (1986b) notes that velox is restricted to the eastern gravel plains in the Namib Desert. Nests of the species are inconspicuous and normally have only one entrance hole. A semilunar crater of excavated material may occur near the nest entrance. He adds that velox is a diurnal insectivore which scavenges dead arthropods, but it will also prey on termites of the genus Hodotermes when eruptions of the latter occur.

Identification

A member of the velox group. Bolton and Marsh (1989) - The type-material and few samples of velox earlier available for examination (Bolton, 1981) all showed the same colour pattern. The alitrunk was dull red to blackish red, the head a lighter red, and the gaster lighter still, orange or even yellow in some individuals. Collections made by Alan Marsh in the Namib Desert at Etosha, in the Naukluft Mountains, and at 23 deg. 23 min. S., 15 deg. 32 min. E., show some velox with this colour pattern but others darker. In the latter the head is red but the remainder of the body is uniformly reddish black to black. Specimens collected by Hamish Robertson in the Namib Naukluft Park are the same as this dark material of Marsh's, but an even darker specimen, collected by H. Schlagbauer in the Brandburg Mountains, also has the head reddish black. Cephalic sculpture is also variable in intensity. It is usually quite faint but in some individuals it may be more strongly developed and conspicuous.

Bolton (1981) - O. velox is one of the seven known species in this genus which lack a conspicuous semicircular impression in the middle of the anterior clypeal margin. The others are Ocymyrmex turneri, Ocymyrmex laticeps, Ocymyrmex cursor, Ocymyrmex ankhu, Ocymyrmex zekhem and Ocymyrmex cavatodorsatus. Of these turneri is a small shiny species with large eyes which break the outline of the sides of the head, and cursor and laticeps have the dorsum of the head strongly sculptured and have the first gastral tergite constricted into a narrow neck basally. O. cavatodorsatus shares most characters with velox, but the shape of the alitrunk is very different; besides this cavatodorsatus is much smaller and has the sculpture of the alitrunk much reduced. Separation of velox from ankhu and zekhem is discussed under those species.

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Afrotropical Region: Angola, Namibia (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

Nomenclature

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

  • velox. Ocymyrmex velox Santschi, 1932a: 387 (w.) NAMIBIA. Bolton, 1981b: 261 (q.). See also: Bolton, 1981b: 280; 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

Bolton (1981) - TL 10.0-10.7, HL 2.20-2.40, HW 2.08-2.30, CI 95-97, SL 2.10-2.29, SI 101-105, PW 1.30-1.42, AL 2.48-2.96 (8 measured).

Large species; anterior clypeal margin entire or very feebly eroded medially giving a weakly crenellated appearance, without a median semicircular impression. Maximum diameter of eyes 0.40-0.43, about 0.19-0.20 x HW. Frontal lobes distinctly convergent posteriorly, the occipital margin indented medially in full-face view. Antennal scapes relatively long, SI above. Promesonotum forming an even low convexity in profile which may be somewhat flattened above in some individuals. Propodeal dorsum more or less flat, usually sloping shallowly downwards posteriorly to the evenly rounded junction with the declivity; the alitrunk not saddle-shaped. Metapleural lobes low and rounded. Petiole node relatively large in profile, high, dome-like and evenly rounded, the anterior peduncle without a ventral process. In dorsal view the petiole node longer than broad. Postpetiole in dorsal view slightly broader than long. Base of first gastral tergite in dorsal view not forming a narrow bottle-neck-like constriction. The tergite basally is no wider than the post petiole but the sides diverge evenly from immediately behind the articulation. Sculpture of head very feeble, faint and even effaced in places, at most consisting of a few weak and superficial irregular rugulae. Ground-sculpture where present only of a weak superficial patterning or shagreening. Dorsal alitrunk transversely rugulose, with or without a patch of longitudinal sculpture on the pronotum and between the mesothoracic spiracles. Rugulae on the propodeal dorsum may be irregular or broken. Petiole and postpetiole dorsally only with superficial patterning, or the former with faint rugular vestiges. Ventral surface of petiole with weak transverse rugulae which may extend up the sides of the node and onto the dorsum, but these are vestigial in some individuals. Dorsal surfaces of head and alitrunk with hairs but these are very rare or even absent on the first gastral tergite. Alitrunk dull red to blackish red, the head a lighter red and the gaster lighter still, orange or even yellow in some individuals.

Type Material

Syntype workers, South West Africa: Otjimbimbi, Kunene R., iii.1923 (G. Arnold) (Naturhistorisches Museum Basel, NM - Bulawayo) [examined].

References