| Ocymyrmex alacer|
Bolton & Marsh, 1989
Bolton (Bolton and Marsh 1989) has observed from dissections that the ergatiod like queens of this species have larger, and many more, ovaries than workers.
A member of the hirsutus group. O. alacer is closely related to Ocymyrmex sphinx, but workers and ergatoid females of these two large species can be separated by characters of the petiole and the pilosity. The form of the petiole in alacer workers is quite different from that of sphinx. In sphinx the node in profile is low and rounded dorsally, and is encircled by rugular sculpture. In dorsal view the sides of the node are rounded and evenly convex, not projecting as triangular prominences as they do in alacer. The posterior face of the node is not flattened in sphinx. Pilosity is conspicuously shorter and much less abundant in sphinx. On the propodeal dorsum the longest hairs are distinctly shorter than the length of the spiracle, and those on the pleurae are very short and less conspicuous. (Bolton and Marsh 1989)
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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.
The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.
- alacer. Ocymyrmex alacer Bolton & Marsh, 1989: 1290, fig. 9 (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.
Holotype. TL 9.8, HL 2.24, HW 2.12, CI 95, SL 2.10, SI 99, PW 1.38, AL 3.04.
Large species. Anterior clypeal margin with a conspicuous median impression which is flanked by a pair of short triangular teeth. On each side of the teeth, and confluent with them, a narrow smooth lamella extends along the anterior clypeal margin almost to the level of the anterior tentorial pit. With the head in full-face view the eyes conspicuously fail to break the outline of the sides of the head. Maximum diameter of eye 0.44, about 0.21 x HW. Sides of head weakly divergent from level of eyes to clypeus. Behind the level of the eyes the sides convex and converging posteriorly, rounding very broadly and evenly into the occipital margin; the latter shallowly convex and weakly indented medially. Promesonotum rounded and convex in profile. Propodeal dorsum weakly sloping posteriorly, rounding very broadly into the declivity, which is shallowly convex above the level of the metapleural lobes. In profile the bulla of the metapleural gland not concealing the metapleural lobes, the latter short and not strongly prominent. Peduncle of petiole weakly sinuate ventrally, lacking a conspicuous ventral process. Node short and low, its dorsal outline broadly triangular in profile. In dorsal view the node much broader than long, flattened behind its highest point and its central portion strongly expanded laterally on each side so that the median section of the node projects as a blunted triangular prominence on each side. Maximum width of petiole node about 0.60, approximately three times wider than the length of the posterior petiolar peduncle, and more than four times wider than the anterior peduncle at its narrowest point. Postpetiole in dorsal view fractionally longer than broad, broadening from front to back. Sternite of postpetiole with a marked median longitudinal impression running its length. Base of first gastral tergite narrowed in dorsal view, no broader than the postpetiole. In profile the first gastral tergite outline more or less flat basally, the first sternite very shallowly concave. Dorsum of head finely, densely and irregularly longitudinally rugulose, the rugulae most regular near the cephalic midline. The rugulae arch outwards behind the eyes and are less strongly developed on the occiput than elsewhere. Dorsal alitrunk transversely rugose, the rugae arched on the pronotum; patch between mesothoracic spiracles longitudinally rugose. Sides of alitrunk and propodeal declivity rugose, the sculpture arched-longitudinal on the lateral pronotum, oblique and less regular on the mesopleuron, longitudinal and irregular on the propodeum, transverse on the declivity. Petiole in dorsal view with transverse weak rugulae from mid length of peduncle to node, rugulae stronger on anterior face of node, stronger still and more obviously transverse on posterior face of node. Sides and ventral surface of peduncle predominantly finely reticulate, with some faint transverse rugulae under the node. Postpetiole superficially reticulate everywhere. Pilosity white to silvery, abundant and very dense on all dorsal and lateral surfaces of head and alitrunk; also many conspicuous long hairs present on petiole node and postpetiole. Hairs on gaster much shorter and sparser than on propodeum, the gastral hairs less than half the length of the longest propodeal hairs, the latter at least as long as the propodeal spiracle. Head dull red; alitrunk darker red, almost maroon; gaster lighter, with an orange or yellowish tint.
Paratypes. TL 9.4-9.8, HL 2.20-2.30, HW 2.08-2.20, CI 93-97, SL 2.02-2.12, SI 95-100, PW 1.34-1.40, AL 2.85-3.10 (8 measured).
As holotype but in some the rugular sculpture of the petiole more pronounced. The sides of the head in a few are more strongly divergent anteriorly than in the holotype. Range of eye size is 0.44-0.46, about 0.20-0.21 x HW.
Paratypes. Answering to description of worker; extremely ergatoid as in all females of this genus. Differing from worker in standard features of antennal scape, frontal lobes and cephalic sculpture as mentioned under the diagnosis of this caste, above, and as described in Bolton (1981). Ergatoid females of this species also tend to have the eyes relatively fractionally smaller, and the petiole node broader, than in the workers.
Holotype worker. South Africa: north Cape Prov., Tosca, no. 13. i.1986, (A.C. Marsh) (The Natural History Museum). Paratypes. 4 workers with same data as holotype but no. 1; 5 workers and 4 ergatoid females with same data as holotype but no. 2 (BMNH, South African Museum, Museum of Comparative Zoology).
- Bolton, B.; Marsh, A. C. 1989. The Afrotropical thermophilic ant genus Ocymyrmex (Hymenoptera: Formicidae). J. Nat. Hist. 2 23: 1267-1308 PDF (page 1290, fig. 9 worker, queen described)