Ocymyrmex picardi

A very conspicuous species, the largest known in the genus, picardi appears to be quite widely distributed in southern Africa.

Identification
As the largest species of the genus, its size alone makes picardi unlikely to be confused with any other Ocymyrmex.

Key to Ocymyrmex workers

Distribution based on Regional Taxon Lists
Afrotropical Region: Angola, Botswana, Namibia, South Africa, Zimbabwe.

Biology
Recent observations at Tosca in the northern Cape, South Africa (Bolton and Marsh 1989) indicate that multiplication of colonies is by fission (hesmosis) of an existing nest. In December 1986 a considerable amount of recruitment in one direction was observed from one nest of picardi. Investigation revealed that the ants were relocating to another nest 150m away. The nest from which the ants were being recruited had a large nest disk and midden of arthropod remains and was clearly an old, well established nest. In contrast, the nest to which the ants were moving had a smaller disk and no midden, and appeared to be more recently excavated. Traffic between the two nests continued for a day and thereafter ceased, and normal foraging activity was seen at both nests. Nest structure is similar to Ocymyrmex foreli: one ground 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.

Diet
Observations by Marsh (as stated in Bolton and Marsh, 1989) indicate the diet is 70 per cent arthropods, much of it live termites, and the remainder consists of plant material.

Reproduction
Forder and Marsh (1989) observed from dissections that the ergatiod like queens of this species have larger, and many more, ovaries than workers.

Morphology
Holldobler, Stanton and Engel (1976) reported the discovery of a of a previously undetected gastral exocrine system in workers of O. picardi and a few North American deserticolous ants belonging to the genus Aphaenogaster. Kugler (1978) later named this structure the pygidial gland. The gland consists of a number of cells located under the intersegmental membrane between gastral tergites 3 and 4 ( = abdominal tergites 6 and 7), with ducts through the membrane. In O. picardi and some other myrmicines the gland is associated with a special cuticular area on the base of the pygidium (gastral tergite 4), on the section of the scelerite which in life is overlapped by the apex of the third gastral tergite.

Nomenclature

 *  picardi. Ocymyrmex picardi Forel, 1901d: 306 (w.) ANGOLA. [Also described as new by Forel, 1903e: 561.] Senior synonym of carpenteri: Bolton, 1981b: 275.
 * carpenteri. Ocymyrmex carpenteri Donisthorpe, 1933b: 195 (q., not w.) BOTSWANA. Junior synonym of picardi: Bolton, 1981b: 275.

Worker
Bolton (1981) - TL 11.6-12.6, HL 2.52-2.80, HW 2.44-2.68, CI 93-97, SL 2.30-2.52, SI 90-98, PW 1.60-1.80, AL 3.40-3.68 (20 measured).

Very large species. Anterior clypeal margin with a conspicuous median semicircular impression which is flanked by a small tooth on each side. Maximum diameter of eye 0.46-0.51, about 0.19-0.20 x HW. With the head in full-face view the occipital margin varying from approximately transverse to feebly indented medially. Promesonotum in profile evenly and broadly convex, sloping posteriorly to the propodeal dorsum which, in this species, is not as strongly depressed below the level of the promesonotum as is usual elsewhere in the genus. Propodeal dorsum rounding broadly and evenly into the declivity. Metapleural lobes rounded, visible in profile, not concealed by the bulge of the metapleural glands. Petiole node in dorsal view as broad as or broader than long. Postpetiole slightly longer than broad in dorsal view, discounting the anterior articulatory portion. Base of first gastral tergite narrow, in dorsal view no broader than the postpetiole, but the sides evenly diverging from their junction with the postpetiole, without a roughly parallel-sided neck. Dorsum of head finely, densely and more or less evenly longitudinally costulate, the costulae rarely approximately straight, much more commonly diverging behind towards the occipital corners. Infrequently a few transverse costulae may be present occipitally. Individual costulae commonly irregular, tending to be narrowly sinuate or wavy, especially away from the midline of the dorsum. Ground-sculpture a fine dense punctulation. Dorsal alitrunk and propodeal declivity transversely rugose except for the space between the mesothoracic spiracles and part of the pronotal dorsum, where sculpture is longitudinal to oblique. Sides of alitrunk rugose, the sculpture less regular on the pleurae than on the sides of the pronotum. Petiole with transverse rugae ventrally, below the node, and also with a few dorsally on the peduncle in front of the node. On the node itself sculpture is usually restricted to a superficial patterning with vestigial rugulae, but occasionally one or two stronger transverse rugulae may be present dorsally, or vertically on the sides, or both. Postpetiole unsculptured except for superficial patterning. All dorsal surfaces of body with scattered strong dark hairs which are reddish brown to blackish; those on the first gastral tergite very sparse and much shorter than those on the alitrunk. Colour very dark red to black, the head usually slightly lighter in shade than the alitrunk and the gaster generally darker.

Type Material
Bolton (1981):

Lectotype worker, Angola: Mossamedes, Cubango-Cuito, here designated [examined].

Ocymyrmex carpenteri Holotype female [not worker], Botswana: Ngamiland, ix.1930-i.1931 (G. D. H. Carpenter) [examined].

The number of specimens in the original syntypic series of picardi was not stated by Forel. At the time of this study only two specimens, mounted on a single pin, were found bearing the label 'typus'. Of these the top specimen is a worker and fits the original description perfectly; it is here designated as lectotype of picardi. The lower specimen, now remounted on a separate pin, is a female and is not mentioned in the original description.

The female (queen) of picardi was first described by Donisthorpe as a worker, under the name of carpenteri. The holotype matches the female in the same series as the picardi lectotype and the synonymy is thus absolute. The female of picardi fits the description given above and its dimensions fall within the ranges given. The only differences from the worker lie in those characters discussed under the generic diagnosis, namely the broader straighter margins to the frontal lobes, broader antennal scapes and sharp transverse sculpture on the posterior portion of the dorsum of the head.