Trichomyrmex oscaris

A widely distributed and versatile species which ranges over most of the Afrotropical region outside the rainforest zone or within that zone in cleared areas. Arnold (1916) records that in Zimbabwe it nests under stones along with a small species of termite, but that the galleries of the two are not interconnected. In Nigeria I have found oscaris in termitaria and nesting in the earth, but on one occasion a nest was found in an old and rotting cocoa pod which was still attached to the tree, some distance above the ground. (Bolton 1987) In Benin, Taylor et al. (2018) report this species from mango (Mangifera indica) orchards. It is ground nesting.

Identification
Bolton (1987) - The closest relative of oscaris appears to be the pantropical tramp-species destructor, but the two are separable by the shape of the petiole node in dorsal view, especially in larger workers. In Trichomyrmex destructor the node is globular to subglobular but in oscaris it is strongly anteroposteriorly compressed and markedly transverse. Also, at any given worker size, the scapes tend to be longer in destructor than in oscaris.

Distribution based on Regional Taxon Lists
Afrotropical Region: Botswana, Burkina Faso, Democratic Republic of Congo, Eritrea, Ethiopia, Ghana, Nigeria, Senegal, South Africa, Uganda, United Republic of Tanzania, Zimbabwe.

Nomenclature

 * . Monomorium oscaris Forel, 1894b: 86 (w.) ETHIOPIA.
 * Type-material: holotype worker.
 * Type-locality: Ethiopia (“Südabessinien”): (no further data) (A. Ilg).
 * Type-depository: MHNG.
 * Combination in Trichomyrmex: Ward, et al. 2015: 76.
 * Status as species: Emery, 1901e: 61; Arnold, 1916: 229; Emery, 1922e: 173; Wheeler, W.M. 1922a: 865; Finzi, 1939a: 164; Ettershank, 1966: 91; Bolton, 1987: 326 (redescription); Bolton, 1995b: 265; Madl, 2019: 16.
 * Senior synonym of bulawayense: Bolton, 1987: 327.
 * Senior synonym of despecta: Bolton, 1987: 327; Bolton, 1995b: 265.
 * Senior synonym of dispar: Bolton, 1987: 326; Bolton, 1995b: 265.
 * Senior synonym of kalahariense: Bolton, 1987: 326; Bolton, 1995b: 265.
 * Senior synonym of prossae: Bolton, 1987: 327; Bolton, 1995b: 265.
 * Senior synonym of solleri: Bolton, 1987: 326; Bolton, 1995b: 265.
 * Distribution: Botswana, Democratic Republic of Congo, Eritrea, Ethiopia, Ghana, Nigeria, Senegal, South Africa, Tanzania, Uganda, Zimbabwe.
 * bulawayense. Monomorium amblyops r. bulawayense Forel, 1914d: 247 (w.) ZIMBABWE.
 * Type-material: syntype workers (number not stated).
 * Type-locality: Zimbabwe (“Rhodesia”): Bulawayo, Hillside, 8.ii.1914, no. 270 (A.M. Macgregor).
 * Type-depository: MHNG.
 * Arnold, 1916: 237 (q.m.).
 * [Junior primary homonym of Monomorium (Mitara) exiguum var. bulawayensis Forel, 1913j: 217.]
 * Subspecies of amblyops: Arnold, 1916: 236.
 * Replacement name: Monomorium amblyops r. prossae Forel, 1916: 418.
 * Junior synonym of oscaris: Bolton, 1987: 327.
 * despecta. Monomorium (Parholcomyrmex) destructor var. despecta Menozzi, 1931a: 154.
 * Type-material: syntype workers (number not stated).
 * Type-locality: Eritrea: Ghinda (K. Escherich).
 * Type-depository: MHNG.
 * [First available use of Monomorium destructor subsp. kalahariense var. despecta Forel, 1910c: 252 (w.) ERITREA; unavailable (infrasubspecific) name (Bolton, 1987: 326).]
 * Forel, 1913b: 331 (q.).
 * As unavailable (infrasubspecific) name: Forel, 1913b: 331; Emery, 1922e: 180; Wheeler, W.M. 1922a: 874; Viehmeyer, 1923: 91; Ettershank, 1966: 88.
 * Subspecies of destructor: Finzi, 1939a: 164.
 * Junior synonym of oscaris: Bolton, 1987: 327; Bolton, 1995b: 261.
 * dispar. Monomorium dispar Emery, 1895h: 24 (w.) SOUTH AFRICA.
 * Type-material: syntype workers (number not stated).
 * Type-locality: South Africa: Transvaal, Makapan, i.-iv.1893 (E. Simon).
 * Type-depository: MSNG.
 * Combination in M. (Parholcomyrmex): Wheeler, W.M. 1922a: 874.
 * Status as species: Arnold, 1916: 235; Emery, 1922e: 180; Wheeler, W.M. 1922a: 874; Ettershank, 1966: 88.
 * Junior synonym of oscaris: Bolton, 1987: 326; Bolton, 1995b: 261.
 * kalahariense. Monomorium destructor subsp. kalahariense Forel 1910c: 252 (w.) BOTSWANA.
 * Type-material: syntype workers (number not stated).
 * Type-locality: Botswana: Kalahari, Kooa-Sekgoma (L. Schultze).
 * Type-depository: MHNG.
 * [Also described as new by Forel 1910f: 18]
 * Forel, 1913b: 331 (q.).
 * Subspecies of destructor: Forel, 1913b: 331; Arnold, 1916: 235; Wheeler, W.M. 1922a: 874; Emery, 1922e: 180; Viehmeyer, 1923: 91; Ettershank, 1966: 90.
 * Junior synonym of oscaris: Bolton, 1987: 326; Bolton, 1995b: 263.
 * prossae. Monomorium amblyops r. prossae Forel, 1916: 418.
 * Replacement name for Monomorium amblyops r. bulawayense Forel, 1914d: 247. [Junior primary homonym of Monomorium (Mitara) exiguum var. bulawayensis Forel, 1913j: 217.]
 * Combination in M. (Parholcomyrmex): Wheeler, W.M. 1922a: 873.
 * Subspecies of amblyops: Wheeler, W.M. 1922a: 873; Arnold, 1926: 232; Ettershank, 1966: 91.
 * Status as species: Emery, 1922e: 173; Prins, 1963: 103.
 * Junior synonym of oscaris: Bolton, 1987: 327; Bolton, 1995b: 266.
 * solleri. Rhoptromyrmex solleri Forel, 1910e: 430 (q.) SENEGAL.
 * Type-material: holotype queen.
 * Type-locality: Senegal: Bissao (Soller).
 * Type-depository: MHNG.
 * Combination in Monomorium: Ettershank & Brown, 1964: 18.
 * Status as species: Wheeler, W.M. 1922a: 909; Emery, 1924d: 290; Ettershank, 1966: 92.
 * Junior synonym of oscaris: Bolton, 1987: 326; Bolton, 1995b: 267.

Bolton (1987) - It is possible that the names ominosa and atomaria, both described from East Africa and subsequently synonymized with destructor, may represent early records of oscaris. However, as the original descriptions are so poor, and as the specimens involved seemingly have long since disappeared, there is no way of proving this; in consequence they are left undisturbed as junior synonyms of destructor. The West African population of oscaris may eventually prove to be separable at species-level from the eastern and southern population. Females of the western population, which correspond to the name solleri in the above synonymy, are lighter in colour and tend to have the mesoscutum relatively broad. The largest workers from this area tend to show faint cephalic sculpture. The amassing of more material will be necessary before a meaningful analysis of these features can be undertaken.

Worker
Bolton (1987) - TL 1.6-3.8, HL 0.46-0.94, HW 0.36-0.84, CI 76-90, SL 0.34-0.54, SI 63-94, PW 0.24-0.52, AL 0.48-1.00 (30 measured).

Workers showing marked size variation in any given series, and displaying monophasic allometric variation. Mandibles with 3 strong teeth, the fourth (basal) tooth reduced to a minute offset denticle or even lost in the smallest workers. Mandibles frequently showing longitudinal rugular sculpture but often smooth. Usually larger workers have the mandibles more strongly sculptured than smaller individuals, but this is by no means universal. Eyes relatively small, the maximum diameter 0.13-0.19 x HW and with 3-6 ommatidia in the longest row. Eyes of larger workers have more ommatidia than those of smaller workers but are smaller in relation to the size of the head. In small workers, with HW < 0-60, the eyes are approximately 0-15-0-19 x HW, whilst in workers with HW > 0.60 the eyes range 0-13-0-16 x HW. In large workers CI is higher than in small, the heads being relatively broader. Antennal scapes relatively longer in small workers and shorter in large workers, as follows.

When HW 0-35-0-45 then SI is 94-84;

when HW 0-45-0-55 then SI is 84-79;

when HW 0-55-0-65 then SI is 76-69;

when HW 0-65-0-75 then SI is 74-64;

when HW 0-75-0-85 then SI is 65-63.

When laid straight back from their insertions the scapes almost reach the occipital margin in smallest workers but fall far short of the margin in the largest individuals. With the head in full-face view the sides shallowly convex and the occipital margin shallowly concave in large workers; in small workers the sides and occipital margin tend to become straighter. Alitrunk in profile with promesonotum convex, the metanotal groove impressed. In dorsal view the petiole node conspicuously anteroposteriorly compressed in large workers, distinctly much broader than long. Postpetiole in dorsal view broader than long. Occipital margin of head with 2-4 or more pairs of standing hairs forming a transverse row. Dorsum of head in front of this row but behind the frontal lobes with 1-4 pairs of standing hairs straddling the midline. Pubescence on head sparse, directed towards the midline. Promesonotal dorsum always with numerous standing hairs; such hairs also present on propodeum in large to medium workers but sometimes absent in small individuals. Petiole, postpetiole and gaster each with numerous elongate backward directed hairs.

Sculpture usually absent from cephalic dorsum, the surface glassy smooth between scattered hair-pits. Medium to large workers with a band of fine transverse striolate sculpture on the rim of the descending occipital surface of the head; this band of weak sculpture usually just visible in full-face view along the rim of the occipital margin. In smaller workers this transverse occipital sculpture is much reduced or absent. Largest workers in some West African samples with the cephalic dorsum showing very fine vestiges of sculpture between the hair-pits. Propodeal dorsum always finely transversely striolate to transversely rugulose; fainter in smaller workers than in larger. Promesonotal dorsum usually smooth with scattered hair-pits, but faint scratch-like or patchy striolate sculpture occurs in the large workers of some samples; a small patch of superficial punctulation may occur at the pronotal-mesonotal junction. Sides of pronotum smooth to vestigially striolate, the remainder of the lateral alitrunk punctuate to reticulate-punctate. First gastral tergite smooth except for hair-pits. Colour yellow to light brownish yellow, glossy.

Type Material
Bolton (1987) - Holotype worker, ETHIOPIA: 'Sudabessinien' (Ilg) [examined].

References based on Global Ant Biodiversity Informatics

 * Arnold G. 1916. A monograph of the Formicidae of South Africa. Part II. Ponerinae, Dorylinae. Annals of the South African Museum. 14: 159-270.
 * Bolton B. 1987. A review of the Solenopsis genus-group and revision of Afrotropical Monomorium Mayr (Hymenoptera: Formicidae). Bulletin of the British Museum (Natural History). Entomology 54: 263-452.
 * Brown W. L., Jr. 1964. Monomorium solleri, new synonymy of, and brief characterization. Pilot Regist. Zool. Card No. 18.
 * Diame L., B. Taylor, R. Blatrix, J. F. Vayssieres, J. Y. Rey, I. Grechi, and K. Diarra. 2017. A preliminary checklist of the ant (Hymenoptera, Formicidae) fauna of Senegal. Journal of Insect Biodiversity 5(15): 1-16.
 * Dieng M. M., A. B. Ndiaye, C. T. Ba, and B. Taylor. 2016. Les fourmis (Hymenoptera, Formicidae) de l’enclos d’acclimatation de Katane de la reserve de faune du Ferlo nord (Senegal). Int. J. Biol. Chem. Sci. 10(4): 1626-1636.
 * Ettershank G. 1966. A generic revision of the world Myrmicinae related to Solenopsis and Pheidologeton (Hymenoptera: Formicidae). Aust. J. Zool. 14: 73-171.
 * Ettershank G., and W. L., Jr., Brown.1964. Monomorium solleri comb. nov. Pilot Regist. Zool. Card No. 18.
 * Finzi B. 1939. Materiali zoologici dell'Eritrea raccolti da G. Müller durante la spedizione dell'Istituto Sieroterapico Milanese e conservati al Museo di Trieste. Parte III. Hymenoptera: Formicidae. Atti del Museo Civico di Storia Naturale di Trieste 14: 153-168.
 * Forel A. 1910. Ameisen aus der Kolonie Erythräa. Gesammelt von Prof. Dr. K. Escherich (nebst einigen in West-Abessinien von Herrn A. Ilg gesammelten Ameisen). Zoologische Jahrbücher. Abteilung für Systematik, Geographie und Biologie der Tiere 29: 243-274.
 * Forel A. 1910. Zoologische und anthropologische Ergebnisse einer Forschungsreise im westlichen und zentralen Südafrika ausgeführt in den Jahren 1903-1905 von Dr. Leonhard Schultze. Vierter Band. Systematik und Tiergeographie. D) Formicidae. Denkschriften der Medizinisch-Naturwissenschaftlichen Gesellschaft zu Jena 16: 1-30.
 * Forel A. 1914. Formicides d'Afrique et d'Amérique nouveaux ou peu connus. Bulletin de la Société Vaudoise des Sciences Naturelles 50: 211-288.
 * IZIKO South Africa Museum Collection
 * Kouakou L. M. M., K. Yeo, K. Ouattara, W. Dekoninck, T. Delsinne, and S. Konate. 2018. Investigating urban ant community (Hymenoptera: Formicidae) in port cities and in major towns along the border in Côte d’Ivoire: a rapid assessment to detect potential introduced invasive ant species. Journal of Animal and Plant Sciences 36(1): 5793-5811.
 * Kouakou L. M. M., W. Dekoninck, M. Kone, T. Delsinne, K. Yeo, K. Ouattara, and S. Konate. 2018. Diversity and distribution of introduced and potentially invasive ant species from the three main ecoregions of Côte d’Ivoire (West Africa). Belgian Journal of Zoology 148 (1): 83–103.
 * Kusnezov N. 1949. El género Monomorium (Hymenoptera, Formicidae) en la Argentina. Acta Zoologica Lilloana 7: 423-448.
 * Madl M. 2019. Notes on the ant fauna of Eritrea (Insecta: Hymenoptera: Formicidae): type specimens deposited in the Natural History Museum Vienna (Austria) and a preliminary checklist. Ann. Naturhist. Mus. Wien, B 121: 9-18.
 * Medler J. T. 1980: Insects of Nigeria - Check list and bibliography. Mem. Amer. Ent. Inst. 30: i-vii, 1-919.
 * Menozzi C. 1931. Spedizione del Barone Raimondo Franchetti in Dancalia. Hymenoptera Formicidae. Annali del Museo Civico di Storia Naturale Giacomo Doria. 55: 154-156.
 * Prins A. J. 1963. A list of the ants collected in the Kruger National Park with notes on their distribution. Koedoe 6: 91-108.
 * Prins A. J. 1964. Revised list of the ants collected in the Kruger National Park. Koedoe 7: 77-93.
 * Taylor B. 1980. Ants of the Nigerian Forest Zone (Hymenoptera: Formicidae). IV. Myrmicinae (Myrmecinini to Tetramoriini). Cocoa Research Institute of Nigeria Research Bulletin 7: 1-63.
 * Taylor B., N. Agoinon, A. Sinzogan, A. Adandonon, Y. N'Da Kouagou, S. Bello, R. Wargui, F. Anato, I. Ouagoussounon, H. Houngbo, S. Tchibozo, R. Todjhounde, and J. F. Vayssieres. 2018. Records of ants (Hymenoptera: Formicidae) from the Republic of Benin, with particular reference to the mango farm ecosystem. Journal of Insect Biodiversity 8(1): 006–029.
 * Wheeler W. M. 1922. Ants of the American Museum Congo expedition. A contribution to the myrmecology of Africa. VIII. A synonymic list of the ants of the Ethiopian region. Bulletin of the American Museum of Natural History 45: 711-1004