Ocymyrmex resekhes

AntWiki - Where Ant Biologists Share Their Knowledge
Jump to: navigation, search
Ocymyrmex resekhes
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Crematogastrini
Genus: Ocymyrmex
Species: O. resekhes
Binomial name
Ocymyrmex resekhes
Bolton & Marsh, 1989

Ocymyrmex resekhes casent0900411 p 1 high.jpg

Ocymyrmex resekhes casent0900411 d 1 high.jpg

Specimen Labels

Nothing is known about the biology of Ocymyrmex resekhes.

Identification

A member of the hirsutus group. O. resekhes is separated here as a sibling species of the more widely distributed Ocymyrmex flaviventris; both show the dense abundant pilosity of the hirsutus-group. The two are basically very similar indeed, but differ in the relative length of the petiolar peduncle, shape of the peduncle anteriorly, and width of the petiole node. In resekhes the petiolar peduncle is long and narrow in profile, tapering more or less evenly anteriorly to the junction with the alitrunk. The anteroventral portion of the peduncle is not suddenly deflected upwards near to the articulation with the alitrunk. In dorsal view the petiole node tends to be elongate and narrow, usually as long as broad or even slightly longer than broad. A few specimens have the node broader than long, but this widening is not nearly so pronounced as in flaviventris. The petiole peduncle is flaviventris is short and stout in profile and the anteroventral margin of the peduncle is suddenly deflected upwards near the articulation with the alitrunk. Sometimes the ventral margin of the peduncle immediately behind this is convex, enhancing the effect. The petiole node in dorsal view is always very conspicuously much broader than long. Some variations in shape occur in the outline profiles of the petiole in both species. Finally, workers of flaviventris average smaller than those of resekhes, and apparently always have shorter scapes. (Bolton and Marsh 1989)

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

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

Distribution based on AntMaps

AntMapLegend.png

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.

  • resekhes. Ocymyrmex resekhes Bolton & Marsh, 1989: 1301, fig. 17 (w.q.) SOUTH AFRICA.

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 8.6, HL 1.98, HW 1.88, CI 95, SL 1.82, SI 97, PW 1.22, AL 2.50.

Palp formula 3, 3 (dissection of paratypes). Median clypeal notch conspicuous, flanked by a triangular tooth-like prominence at each side. Eyes just failing to break the outline of the sides of the head in full-face view; maximum diameter of eye 0.22 x HW. Sides of head convergent posteriorly, especially behind the eyes where they round broadly and evenly into the occipital margin. Median impression of the occipital margin vestigial. In front of level of eye the sides less convex than posteriorly, only feebly divergent anteriorly. With alitrunk in profile the pronotal dorsal outline somewhat flattened, not evenly convex, ascending posteriorly to the convex mesonotum which slopes posteriorly down to the propodeum. Metapleural lobes small and rounded, but visible in profile, projecting beyond the bulge of the metapleural gland bulla. Peduncle of petiole long and narrow, tapering anteriorly, its anteroventral surface not suddenly deflected upwards close to the articulation with the alitrunk. Petiole node in profile low and rounded, in dorsal view narrow and somewhat longer than broad. Postpetiole in dorsal view longer than broad. Base of gaster in dorsal and lateral view distinctly constricted; the base of the first tergite slightly narrower than the postpetiole in dorsal view. Cephalic dorsum finely and very densely longitudinally costulate. The costulae centrally on the head running straight back towards the occiput, but those in front of the eyes oblique. The costulae themselves are somewhat irregular, not straight, but without large vermiculate areas and the head lacking areas of chaotic sculpture. Sides of pronotum weakly longitudinally costulate, remainder of side of alitrunk obliquely rugulose. Transversely arched costulae on pronotal dorsum very weak, almost obliterated in places. A small patch of longitudinal sculpture is present between the mesothoracic spiracles but behind this the dorsal alitrunk is uniformly transversely rugulose, as is the propodeal declivity. Petiole ventrally with short transverse rugulae, which also occur dorsally on the peduncle, but elsewhere on petiole sculpture is reduced to a fine granulation or superficial reticulation. Postpetiole everywhere with fine superficial sculpture everywhere. Pilosity on head and alitrunk dorsum conspicuous and dense, the dorsal alitrunk with numerous short elevated hairs between the longer main components of the pilosity. Mesopleura and metapleura densely clothed with outstanding hairs, almost with a furry appearance. Colour of head and alitrunk a very dull dark red, the gaster lighter, orange-red to yellowish.

Paratypes. TL 7.9-8.6, HL 1.74-2.00, HW 1.66-1.96, CI 95-99, SL 1.66-1.90, SI 95-101, PW 1.06-1.23, AL 2.28-2.60 (20 measured).

As holotype but some with pronotal dorsal outline more flattened, and some with the outline somewhat more evenly convex. Cephalic sculpture variable. Many as holotype but some with the fine longitudinal costulae more disorganized, wavy or even broken in places. A distinct punctulate ground-sculpture may occur, especially close to the inner margins of the eyes, and in a few workers this may become the dominant sculpture of the immediate area. In some the longitudinal costulae become disorganized posteriorly, in others they tend to weaken or even fade out as they approach the occipital margin. Sides of pro no tum frequently with more strongly developed costulae than those exhibited by the holotype, and the sculpture of the pronotal dorsum is often also better defined. Maximum diameter of eye 0.21-0.23 x HW.

Holotype Specimen Labels

Type Material

Holotype worker, South Africa: north Cape Prov., Andriesvale, sample NC7F, 1986 (A.C. Marsh) (The Natural History Museum). Paratypes, 2 workers with same data as holotype; 18 workers and one ergatoid female with same data as holotype but samples NC7C, NC7E, NC7K, NC7M (BMNH, South African Museum, Museum of Comparative Zoology).

References