Ocymyrmex ignotus

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

Ocymyrmex ignotus casent0900408 p 1 high.jpg

Ocymyrmex ignotus casent0900408 d 1 high.jpg

Specimen Labels

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.

Identification

A member of the hirsutus group, ignotus displays the abundant dense pilosity and other characteristics of the group. Species most closely related to ignotus include Ocymyrmex flaviventris and Ocymyrmex resekhes. O. ignotus separates from both of these by having the gaster very dark in colour, blackish and darker than the head and alitrunk as opposed to yellowish or orange and lighter than the head and alitrunk in flaviventris and resekhes. Also, the postpetiole in ignotus is voluminous and has a swollen appearance, with a markedly convex ventral outline. O. ignotus averages larger than flaviventris and has a broader head. It also has a long narrow petiolar peduncle, rather than the short stout peduncle exhibited by flaviventris. The petiole node of ignotus is much broader in dorsal view than that of resekhes and the vermiculate to chaotic areas of cephalic sculpture characteristic of ignotus do not occur in resekhes. (Bolton 1981)

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Afrotropical Region: South Africa (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

Nomenclature

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

  • ignotus. Ocymyrmex ignotus Bolton & Marsh, 1989: 1297 (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 8.3, HL 1.90, HW 1.90, CI 100, SL 1.76, SI 93, PW 1.22, AL 2.56.

Notch in anterior clypeal margin deep and conspicuous, flanked by a pair of sharp teeth. Palp formula 3, 3. Maximum diameter of eye 0.38, about 0.20 x HW, the eyes distinctly failing to break the outline of the sides of the head in full-face view. Sides of head weakly divergent in front of the eyes, behind the eyes rounding broadly into the occipital margin; the latter feebly indented medially. With alitrunk in profile the meta pleural lobes conspicuous, projecting posteriorly and not concealed by the meta pleural gland bulla. Petiole in profile with an elongate anterior peduncle and a narrowly rounded node. In dorsal view the node stocky and broad, distinctly much broader than long and its maximum width strikingly greater than that of the posterior peduncle (ca 0.44 and 0.32 respectively). Postpetiole in profile swollen, broadly convex both dorsally and ventrally and very much more voluminous than the petiole. Base of gaster strongly constricted. Dorsum of head finely densely and strongly sculptured everywhere. Centrally the head with a longitudinal strip of irregular close-packed rugulae behind the frontal lobes. On each side of this, to the inner margins of the eyes, the surface is blanketed by fine and very dense vermiculate to chaotic rugulae. Dorsal alitrunk transversely rugulose to rugose except for a longitudinally sculptured patch between the meso thoracic spiracles. Sides of alitrunk strongly rugulose to rugose, the sculpture finer on the pronotum than elsewhere. Petiole with transverse rugulae ventrally, but these fading out on the sides of the node, leaving these areas and the dorsum finely shagreenate to superficially reticulate. Postpetiole and first gastral tergite superficially reticulate to shagreenate. Pilosity dense everywhere, the entire body abundantly hairy. Pleurae and sides of propodeum with dense long projecting pilosity. Gaster black, in places with a very faint dull reddish tint. Remainder of body very dull red, the whole ant appearing blackish to the naked eye.

Paratypes. TL 7.9-8.3, HL 1.84-1.90, HW 1.82-1.92, CI 97-102, SL 1.70-1.76, SI 91-95, PW 1.18-1.22, AL 2.46-2.57 (10 measured).

As holotype but maximum diameter of eye 0.20-0.21 x HW. Most para types the same colour as the holotype but some darker, the alitrunk in these blackish and almost the same shade as the gaster.

Type Material

Holotype worker, South Africa: north Cape Province, Pomfret, xii.1986, NCI2A, (A.C. Marsh) (The Natural History Museum). Paratypes, 17 workers and 2 ergatoid females, with same data as holotype (BMNH, SAM, Museum of Comparative Zoology).

References