| Ocymyrmex phraxus|
Nothing is known about the biology of Ocymyrmex phraxus.
A member of the weitzeckeri group. Bolton and Marsh (1989) - In the original description the petiole node shape of phraxus was given as “a small node which is not sharply differentiated from the peduncle; the dorsum of the peduncle runs into the anterior face of the node without a marked change in slope.” This character is now known to be variable. The more recently acquired material shows some workers with the node almost as noted above, some with the anterior slope of the node obviously differentiated from the peduncle, and some of an intermediate shape.
Bolton (1981) - The non-paratypic series matches the type-series well but has sculpture slightly more intense in development and has some workers which are slightly smaller, HL 1.78-1.90, HW 1.70-1.82, CI 95-96, SL 1.54-1.64, SI 90-93. The sculpture of the petiole in phraxus is reminiscent of a reduced version of that found in Ocymyrmex sobek, but in the latter the node is greatly swollen and very distinctive, and the gaster is yellowish, much lighter than the alitrunk.
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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.
Known only from the worker caste.
The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.
- phraxus. Ocymyrmex phraxus Bolton, 1981b: 274, fig. 27 (w.) TANZANIA. See also: Bolton & Marsh, 1989: 1301.
Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.
Holotype. TL 7.9, HL 1.92, HW 1.82, CI 95, SL l.58, SI 87, PW l.15, AL 2.32.
Anterior clypeal margin with a deep median impression which is flanked on each side by a tooth. Sides of head in front of eyes more or less parallel, the head not broadening anteriorly. Maximum diameter of eye 0.38, about 0.21 x HW. Promesonotum forming an even, low convexity in profile which slopes gently downwards posteriorly. Propodeal dorsum rounding evenly into the declivity. Metapleural lobes low and rounded. Petiole in profile with a small node which is not sharply differentiated from the peduncle; the dorsum of the peduncle runs into the anterior face of the node without a marked change in slope. This surface is confluent behind with the dorsum, which is low and broadly evenly rounded. In dorsal view the node is narrow and almost parallel-sided, its maximum width not much greater than that of the posterior peduncle. Postpetiole longer than broad in dorsal view, discounting the anterior articulatory section. First gastral tergite constricted basally, forming a narrow neck behind the postpetiole. Dorsum of head densely sculptured with fine, sharply defined parallel longitudinal rugulae which are slightly divergent posteriorly and more divergent laterally where they tend to arch outwards behind the eyes. Spaces between the rugulae filled with a fine dense and conspicuous punctulate ground-sculpture. Pronotum with arched-transverse costulae, with a patch of longitudinal sculpture between the mesothoracic spiracles. Remainder of dorsal alitrunk transversely rugose except for a small disorganized patch between the propodeal spiracles. Alitrunk dorsally lacking the punctulate ground-sculpture seen on the head. Petiole with a number of very fine rugulae which encircle the node, the postpetiole only with fine superficial patterning, or light shagreening. Dorsal surfaces of head and alitrunk all with numerous hairs, those on the first gastral tergite much shorter and sparser than those on the alitrunk. Alitrunk a dark, deep red, dully shining. Head dark red but lighter in shade than the alitrunk, the contrast easily visible to the naked eye. Gaster blackish brown to black, darker than the rest of the body.
Paratypes. TL 7.7-8.0, HL 1.90-1.96, HW 1.80-1.86, CI 94-96, SL 1.56-1.60, SI 85-89, PW 1.14-1.16, AL 2.26-2.34 (5 measured). Maximum diameter of eye 0.36-0.38, about 0.20-0.21 x HW. As holotype but some with the petiole node slightly broader in dorsal view and with the disorganized rugular patch on the propodeal dorsum less obviously developed.
- Bolton, B. 1981b. A revision of six minor genera of Myrmicinae (Hymenoptera: Formicidae) in the Ethiopian zoogeographical region. Bull. Br. Mus. (Nat. Hist.) Entomol. 43: 245-307 PDF (page 274, fig. 27 worker described)
- Bolton, B.; Marsh, A. C. 1989. The Afrotropical thermophilic ant genus Ocymyrmex (Hymenoptera: Formicidae). J. Nat. Hist. 2 23: 1267-1308 PDF