Ocymyrmex tachys

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

Ocymyrmex tachys casent0900417 p 1 high.jpg

Ocymyrmex tachys casent0900417 d 1 high.jpg

Specimen Labels

Nothing is known about the biology of Ocymyrmex tachys.

Identification

A member of the tachys group. The character combination of small size, very reduced palp formula (PF 2,3), medially impressed clypeus, eyes which strongly break the outline of the sides of the head, and unconstricted gaster, renders the tachys-group immediately recognizable. (Bolton and Marsh 1989)

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Afrotropical Region: Namibia (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

Known only from the worker caste.

Nomenclature

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

  • tachys. Ocymyrmex tachys Bolton & Marsh, 1989: 1304 (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 5.2, HL 1.36, HW 1.22, CI 90, SL 1.30, SI 107, PW 0.76, AL 1.60.

Palp formula 2,3; one of only two Ocymyrmex species so far known to have just 2 maxillary palp segments, the other being Ocymyrmex engytachys. Anterior clypeal margin with a conspicuous median impression. With the head in full-face view the eyes very obviously breaking the outline of the sides. Eyes relatively large, the maximum diameter 0.32, about 0.26 x HW. Sides of head in front of eyes straight and weakly divergent anteriorly. Behind the eyes the sides convergent posteriorly and rounding into the transverse occipital margin; the latter not indented nor concave medially. Alitrunk in profile with pro meso no tum evenly convex, the mesonotum sloping posteriorly and confluent with the propodeum, which slopes slightly less steeply backwards. Propodeal dorsum and declivity confluent through a long shallow curve which is only weakly convex and appears almost like a continuation of the dorsum. Bulla of meta pleural gland strongly prominent posteriorly, almost masking the metapleural lobe, the apex of which can just be seen posteriorly. Petiole node in profile evenly rounded, in dorsal view slightly longer than broad. Postpetiole about as long as broad in dorsal view, broadest posteriorly. Postpetiolar sternite ventrally evenly shallowly transversely concave, lacking a strong median longitudinal groove. In profile outline of first gastral tergite shallowly convex basally from its articulation with the postpetiole; first sternite with a more or less flat outline in its basal third. In dorsal view the gaster not strongly constricted nor neck-like basally. Gaster no wider than postpetiole at their point of junction but behind this the sides of the tergite are evenly and distinctively divergent. Dorsum of head finely irregularly longitudinally rugulose, the rugulae faint and feebly divergent posteriorly. Spaces between rugulae with conspicuous granular to punctulate ground-sculpture, which tends to become very weak or to fade out occipitally. Dorsal alitrunk densely and finely regularly transversely rugose except on the pronotum where the sculpture is strongly arched and finer than elsewhere. Sides of alitrunk regularly rugose; longitudinal on pronotum, oblique elsewhere. Petiole mostly finely reticulate but the ventral surface with some transverse rugulae below the node, and the dorsum with some faint to vestigial transverse rugulae on the node. Postpetiole superficially reticulate. First gastral tergite mostly glassy smooth but basally with the faintest traces of fine superficial reticular patterning. All dorsal surfaces of head and body with conspicuous silvery standing hairs, those on the basal half ofthe first gastral tergite about equal in length to those on the propodeal dorsum. Head dark reddish brown, mandibles and head to level of frontal lobes lighter brown. Alitrunk black, gaster intermediate in shade between head and alitrunk.

Paratypes. TL 5.2-5.7, HL 1.36-1.42, HW 1.22-1.31, CI 88-92, SL 1.30-1.40, SI 107-108, PW 0.76-0.84, AL 1.60-1.70 (4 measured).

As holotype but maximum diameter of eye 0.24-0.26 x HW. One paratype is a teneral and light brown in colour. In the remainder the colour of the alitrunk varies from dark brown to black.

Type Material

Holotype worker, Nambia (=South West Africa): Namib Desert, Skeleton Coast, sample SC6, Il.viii.1982, 19 deg. 45 min. S., 13 deg. 23 min. E., gravel outcrop (A.C. Marsh) (The Natural History Museum). Paratypes, 4 workers with same data as holotype (BMNH, South African Museum).

References