Pheidole oxyops

P. oxyops occurs in cerrado (savanna) and the edges of semideciduous forest. In the region of San Antonio de Posse, São Paulo, Fernandes et al. (1994) found the species abundant along the forest edge and in cotton fields. In the latter it was very effective in removing adult boll weevils (Anthonomus grandis) from the ground, accounting in one study period for 90% of the predation due to ants, where predation by ants as a whole destroyed 20% of the weevils. Fernandes et al. use the name P. oliveirai, which I erroneously supplied from an early draft of the manuscript of my monograph; the specimens supplied me and hence the name I erected in manuscript fall under oxyops. (Wilson 2003)

Identification
See the description in the nomenclature section.

Distribution
Kempf (1972b) and I have recorded oxyops, in addition to the type series from Paraguay, from Salta, northern Argentina, and Goiás, Mato Grosso, Minas Gerais, and São Paulo in southeastern and central Brazil. (Wilson 2003)

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Brazil, Paraguay.

Pheidole oxyops builds subterranean nests, with an external architecture that is distinctive and easily recognizable by its wide and specific entrance hole, measuring up to 12.2 cm in diameter, denoting a pitfall-trap. Excavations revealed that the nests are perpendicular relative to the ground, beginning with a cylindrical channel with a mean length of 13.5 cm, containing irregular formations, and whose diameter becomes progressively narrower until the first chamber is formed. As the channel continues, dish-like chambers appear, interconnected by channels that become progressively narrower and longer, while the chambers are arranged at greater distances from each other as nest depth increases. Both channels and chambers are located on the vertical projection of the entrance hole. Nests may reach a depth of up to 5.09 m, with a number of chambers ranging between 4 and 14. (Forti et al., 2007)

Gomes et al. (2019) examined the nesting habits of these ants and provide the following notes:
 * 1) The ant species Pheidole oxyops has the particular behaviour of placing feathers along the edge of entrances to its nests. Here two hypotheses concerning this behaviour were tested: (i) P. oxyops, due to its essentially carnivore diet and particular nest structure (which acts as pitfall traps), uses feathers to enhance the capture of arthropods; and (ii) P. oxyops uses feathers as a strategy for obtaining water, as feathers could act as retainers of night moisture.
 * 2) To test the first hypothesis, two plots with 20 pitfall traps were established, and inside each plot feathers were placed around half of these traps. It was expected that pitfall traps with feathers would collect a larger number of individuals and species of arthropods. To test the second hypothesis, all feathers were removed from 28 nests and water was supplied (wet cotton balls) to half of these nests. It was expected that colonies with access to an artificial water source would collect fewer feathers than control colonies.
 * 3) Only the first hypothesis was supported. Our results indicate that feathers have the potential to enhance prey capture by P. oxyops providing the colonies with a more diverse and abundant diet. The ants’ habit of placing feathers around the nest, which can be considered as a low-cost foraging strategy, could be particularly important during periods of low food resource availability.

Worker
Minor

Nomenclature

 *  oxyops. Pheidole oxyops Forel, 1908c: 377 (s.q.) PARAGUAY. Forel, 1911c: 303 (w.m.). Senior synonym of genalis, regia: Kempf, 1964e: 58. See also: Wilson, 2003: 212.
 * regia. Pheidole oxyops subsp. regia Forel, 1908c: 378 (s.w.) BRAZIL. Forel, 1909a: 258 (q.). Junior synonym of oxyops: Kempf, 1964e: 58.
 * genalis. Pheidole genalis Borgmeier, 1929: 199, pl. 7, fig. 4 (s.w.) BRAZIL. Junior synonym of oxyops: Kempf, 1964e: 58.

Description
From Wilson (2003): A large (major Head Width 1.90 mm), reddish brown member of the diligens group easily distinguished as follows.

Major: head in side view elliptical, tapering equally toward the occiput and clypeus on opposite ends; antennal scape reaches much less than half the distance from eye to occipital corner; in dorsal-oblique view, the two lobes of the pronotum and mesonotal convexity present a profile of three equally spaced convexities, and the propodeal dorsum has a small convexity just anterior to the spine; in side view propodeal spine short, thin, and vertical to propodeal dorsal face; postpetiole from above conulate; no rugoreticulum present anywhere; anterior and parts of lateral margins of pronotum carinulate.

Minor: a neck and nuchal collar present; propodeal spine reduced almost to a denticle.

MEASUREMENTS (mm) Syntype major: HW 1.92, HL 2.12, SL 1.06, EL 0.30, PW 0.80. Syntype minor: HW 0.74, HL 1.02, SL 1.24, EL 0.22, PW 0.54.

COLOR Major and minor: concolorous light brown.



'''Figure. Upper: syntype, major. Lower: syntype, minor. Scale bars = 1 mm.'''

Type Material
PARAGUAY: San Bernadino (Fiebring). and - as reported in Wilson (2003)

Etymology
Gr oxyops, sharp-eyed or sharp-faced, allusion uncertain. (Wilson 2003)

References based on Global Ant Biodiversity Informatics

 * Araujo L. M., and G. W. Fernandes. 2003. Altitudinal patterns in a tropical ant assemblage and variation in species richness between habitats. Lundiana 4(2): 103-109.
 * Bestelmeyer B. T., and J. A. Wiens. 1996. The Effects of Land Use on the Structure of Ground-Foraging Ant Communities in the Argentine Chaco. Ecological Applications 6(4): 1225-40.
 * Borgmeier T. 1929. Zur Kenntnis der brasilianischen Ameisen. EOS. Revista Española de Entomología 5: 195-214.
 * Cividanes F. J., J. C. Barbosa, I. C. F. Martins, F. Pattaro, M. A. Nunes, R. Souza Santos. 2009. Diversity and spatial distribution of ground arthropods in agroecosystems. Bragantia, Campinas, 68(4): 991-1002.
 * Czaczkes, T.J. and F.L.W. Ratnieks. 2011. Simple rules result in the adaptive turning of food items to reduce drag during cooperative food transport in the ant Pheidole oxyops. Insectes Sociaux 58:91-96
 * Czaczkes, T.J., P. Nouvellet and F.L.W. Ratnieks. 2011. Cooperative food transport in the Neotropical ant, Pheidole oxyops. Insectes Sociaux 58:153-161
 * Fernández, F. and S. Sendoya. 2004. Lista de las hormigas neotropicales. Biota Colombiana Volume 5, Number 1.
 * Forel A. 1908. Ameisen aus Sao Paulo (Brasilien), Paraguay etc. gesammelt von Prof. Herm. v. Ihering, Dr. Lutz, Dr. Fiebrig, etc. Verhandlungen der Kaiserlich-Königlichen Zoologisch-Botanischen Gesellschaft in Wien 58: 340-418.
 * Forel A. 1909. Ameisen aus Guatemala usw., Paraguay und Argentinien (Hym.). Deutsche Entomologische Zeitschrift 1909: 239-269.
 * Forel A. 1911. Ameisen des Herrn Prof. v. Ihering aus Brasilien (Sao Paulo usw.) nebst einigen anderen aus Südamerika und Afrika (Hym.). Deutsche Entomologische Zeitschrift 1911: 285-312.
 * Forel A. 1912. Formicides néotropiques. Part III. 3me sous-famille Myrmicinae (suite). Genres Cremastogaster et Pheidole. Mémoires de la Société Entomologique de Belgique. 19: 211-237.
 * Kempf W. W. 1964e. Miscellaneous studies on Neotropical ants. III. (Hymenoptera: Formicidae). Studia Entomologica 7: 45-71.
 * Kempf, W.W. 1972. Catalago abreviado das formigas da regiao Neotropical (Hym. Formicidae) Studia Entomologica 15(1-4).
 * Kusnezov N. 1978. Hormigas argentinas: clave para su identificación. Miscelánea. Instituto Miguel Lillo 61:1-147 + 28 pl.
 * Luederwaldt H. 1918. Notas myrmecologicas. Rev. Mus. Paul. 10: 29-64.
 * Nascimento Santos M., J. H. C. Delabie, and J. M. Queiroz. 2019. Biodiversity conservation in urban parks: a study of ground-dwelling ants (Hymenoptera: Formicidae) in Rio de Janeiro City. Urban Ecosystems https://doi.org/10.1007/s11252-019-00872-8
 * Nogueira Rossi M., and H. G. Fowler. 2004. Predaceous Ant Fauna in New Sugarcane Fields in the State of São Paulo, Brazil. Brazilian Archives of Biology and Technology 47(5): 805-811.
 * Pacheco R., and H. L. Vasconcelos. 2012. Subterranean Pitfall Traps: Is ItWorth Including Them in Your Ant Sampling Protocol? Psyche doi:10.1155/2012/870794
 * Ribeiro L. F., R. R. C. Solar, T. G. Sobrinho, D. C. Muscardi, J. H. Schoereder, and A. N. Andersen. 2019. Different trophic groups of arboreal ants show differential responses to resource supplementation in a neotropical savanna. Oecologia 190(2): 433-443.
 * Santos-Junior L. C., J. M. Saraiva, R. Silvestre, and W. F. Antonialli-Junior. 2014. Evaluation of Insects that Exploit Temporary Protein Resources Emphasizing the Action of Ants (Hymenoptera, Formicidae) in a Neotropical Semi-deciduous Forest. Sociobiology 61(1): 43-51
 * Santschi F. 1925. Nouveaux Formicides brésiliens et autres. Bulletin et Annales de la Société Entomologique de Belgique 65: 221-247.
 * Silvestre R., C. R. F. Brandão, and R. R. Silva da 2003. Grupos funcionales de hormigas: el caso de los gremios del cerrado. Pp. 113-148 in: Fernández, F. (ed.) 2003. Introducción a las hormigas de la región Neotropical. Bogotá: Instituto de Investigación de Recursos Biológicos Alexander von Humboldt, xxvi + 424 pp.
 * Soares S. A., D. Lange, and W. F. Antoniali Junior. 2006. Communities of Epigaeic ants (Hymenoptera: Formicidae) in an area of reforestation and in native forest. Sociobiology 49(3): 251-263.
 * Soares S. A., W. F. Antoniali Junior, and S. E. Lima-Junior. 2010. Diversidade de formigas epigéicas (Hymenoptera, Formicidae) em dois ambientes no Centro-Oeste do Brasil. Revista Brasileira de Entomologia 54(1): 7681.
 * Suguituru S. S., M. Santina de Castro Morini, R. M. Feitosa, and R. Rosa da Silva. 2015. Formigas do Alto Tiete. Canal 6 Editora 458 pages
 * Tofilski, A. and F. L. W. Ratnieks. 2008. Simple rules based on pile slope are used in the self organization of sand pile formation by Pheidole oxyops ants. Insectes Sociaux 55(1):37-42.
 * de Almeida Soares S., Y. R. Suarez, W. D. Fernandes, P. M. Soares Tenorio, J. H. C. Delabie, and W. F. Antonialli-Junior. 2013. Temporal variation in the composition of ant assemblages (Hymenoptera, Formicidae) on trees in the Pantanal floodplain, Mato Grosso do Sul, Brazil. Rev. Bras. entomol. 57: 84-90