Proceratium oceanicum

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Proceratium oceanicum
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Proceratiinae
Tribe: Proceratiini
Genus: Proceratium
Species: P. oceanicum
Binomial name
Proceratium oceanicum
De Andrade, 2003

Proceratium oceanicum P casent0171053.jpg

Proceratium oceanicum D casent0171053.jpg

Specimen Label

Collections have all been from primary or disturbed rainforest.


A member of the silaceum clade.

Hita Garcia et al. (2015) - The following character combination distinguishes P. oceanicum from the remainder of the Proceratium silaceum clade: relatively larger species (HW 0.76–0.78; WL 0.99–1.00); in full-face view head weakly longer than wide (CI 93); lateral expansions of frontal carinae weakly triangular and moderately rounded; petiolar node extremely squamiform (DPeI 680–693) and strongly narrowing from base to apex; subpetiolar process thinly dentiform.

P. oceanicum and Proceratium relictum are highly distinctive species that can be easily distinguished from all other congeners by the extremely squamiform petiolar node. This character, among others, also separates both clearly from the new species Proceratium vinaka. Despite its sympatric occurrence, P. oceanicum and P. relictum are not likely to be confused. The latter is significantly larger in size (HW > 1.00; WL > 1.30), has a noticeably broader head (CI 101), and the subpetiolar process is thickly spiniform, whereas P. oceanicum is conspicuously smaller (HW < 0.80; WL < 1.10), possesses a narrower head (CI 93), and its subpetiolar process thinly dentiform. Additionally, in profile the propodeum of P. oceanicum is rounded while it is weakly, but clearly marginate in P. relictum.

Baroni Urbani, C. and de Andrade, M.L. (2003) - Proceratium oceanicum is a medium-sized dark reddish black species with a strongly squamiform petiolar node, a rounded unmargined propodeum, and an acutely angled subpetiolar process. Proceratium oceanicum is most similar to Proceratium relictum, with which it is sympatric, but can be distinguished by the size, rounded propodeum and lack of a projecting tooth on the subpetiolar process. (Sarnat and Economo 2013)

Keys including this Species


Distribution based on Regional Taxon Lists

Indo-Australian Region: Fiji (type locality).

Distribution based on AntMaps


Distribution based on AntWeb specimens

Check data from AntWeb


Very little is known about the biology of Proceratium ants. They nest in soil, rotten wood, under deep-set stones and, in a few cases, tree branches. For many species the nest consists of small rounded chambers hollowed out of soft rotten wood or in the soil. Toward the cooler limits of the range, particularly in North America, nests and foraging workers are found under deep set rocks instead of in rotten wood. The nest site is usually in forest shade, in old moist gardens, or similar habitats that are constantly moist. Some species of known to be egg predators of arthropods, especially of spiders.

Most Proceratium are relatively rare but this is not the full explanation for why they are not commonly collected. Colonies of most species are small. Based on anectdotal natural history information from a few species, it was once thought that most Proceratium would likely be found to have mature colonies that contain somewhere between 10 - 50 workers. Yet nests with more than 50, and in some cases up to 200, workers have been been reported. Besides small colonies, these ants also do not appear to forage in places where they are readily encountered.

Males and females are though to be produced in small numbers but we generally do not have enough data for colonies of any species to know what might be typical. Reproductive flights have been observered toward the end of the summer in some northern temperate areas. In these regions the nuptial flight occurs during the last half of August. Both sexes climb some distance from the nest entrance before taking flight. Workers too issue from the nest during the nuptial flight, as is often the case with otherwise cryptobiotic ants.



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

  • oceanicum. Proceratium oceanicum De Andrade, in Baroni Urbani & De Andrade, 2003b: 310, fig. 127 (w.) FIJI IS.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.



TL 3.47-3.59; HL 0.78-0.80; HW 0.75-0.78; EL 0.03-0.04; SL 0.54-0.56; WL 0.98-1.00; PeL 0.23-0.24; PeW 0.43-0.47; HFeL 0.63-0.65; HTiL 0.50-0.51; HBaL 0.39; LS4 0.39-0.40; LT4 0.76-0.80; CI 94.9-97.5; SI 68.3-71.8; IGR 0.50-0.52.

Head slightly longer than broad and with the sides gently diverging posteriorly. Vertex in full face view gently convex. Clypeus reduced and as long as the antennal sockets. Anterior border of the clypeus truncate. Frontal carinae closer to each other than in relictum, not covering the antennal insertions. Lateral expansions of the frontal carinae narrower than in relictum, weakly raised, diverging on the two anterior thirds, parallel and lower on the posterior third. Frontal area flat and with a superficial, thin longitudinal cariila. Head anterolaterally with a short, longitudir~al carina. Genal carinae marked, each carina corresponding to the external border of a deep sulcus. Eyes visible as a dark dot below the integument, small and on the middle of the head sides. First funicular joint about 1/4 longer than broad. Funicular joints 2-10 broader than long. Last funicular joint as long as the sum of joints 7-10. Scapes short of the vertexal margin and gently thickening apically. Masticatory margin of the mandibles with 5 denticles before the pointed apical tooth. Palp formula 2,2.

Mesosoma in profile convex and about as long as the maximum head length (mandibles included). Pronotal and propodeal sutures absent. Basal face of the propodeum gently declivous posteriorly. Declivous face of the propodeum sloping posteriorly. Each side of the declivous face of the propodeum not carinate and with a trace of a minute, broad angle. Propodeal spiracle round and above mid height in lateral view.

Petiole squamiform, compressed and weakly carinate dorsally. Anterior border of the petiole straight, without neck and carina. Ventral process of the petiole small, stout and triangular. Postpetiole anteriorly slightly protruding over the petiole; its sides diverging and gently convex posteriorly. Postpetiolar sternite anteromedially with a marked subtriangular projection. Postpetiolar sternite gently convex posteriorly in profile. Constriction between postpetiole and gaster impressed. Gastral tergite I about 1/3 longer than the postpetiole and slightly convex on the curvature. Remaining gastral tergites and sternites curved ventrally.

Legs slender and slightly elongate. All tibiae with a pectinate spur. Spurs of fore legs without basal spine. Fore basitarsi longer than the mid ones. Hind basitarsi about 1/5 shorter than hind tibiae. Second tarsomere of hind legs shorter than pretarsus. Pretarsal claws simple. Arolia absent.

Sculpture. Body more shining than in relictum. Head covered with small piligerous punctures, the punctures denser, larger and mixed with irregular rugosities anterolaterally. Mesosoma, petiole postpetiole, gaster and legs covered by piligerous punctures smaller and sparser than on the posterior part of the head. Lower meso- and metapleurae with variably impressed, irregular, thin rugosities.

Body covered by hairs of three main types: (1) short, dense, suberect or subdecumbent on the whole body, suberect and sparse on the funicular joints; (2) longer than type (1), erect on the whole body, sparse on the scapes, absent on the funiculi; (3) shorter than hair type (1), dense and decumbent on the funicular joints only. In addition the funicular joints bear whitish, thick, appressed, sparse hairs.

Colour. Dark brown with lighter anterior half of the head. Legs dark orange to brown.

Hita Garcia et al. (2015) - (N=2). TL 3.38–3.41; EL 0.03; SL 0.55–0.58; HL 0.81–0.83; HLM 1.00–1.02; HW 0.76–0.78; WL 0.99–1.00; HFeL 0.63; HTiL 0.48–0.50; HBaL 0.38–0.40; PeL 0.63; PeW 0.43; DPeI 680–693; LT3 0.54–0.56; LS4 0.35–0.40; LT4 0.71–0.78; OI 4; CI 93; SI 68–70; IGR 0.49–0.52; ASI 133–139.

Type Material

Holotype worker from Fiji Islands labelled: "Nadarivatu, Viti, Fiji, R. W. Taylor, 16.II.1962, on soil under grass, Rainforest, R. W. Taylor, acc 25", in Australian National Insect Collection.


Oceanicus is a neologism created to indicate the provenance from Oceania.


References based on Global Ant Biodiversity Informatics

  • Baroni Urbani C., and M.L de Andrade. 2003. The ant genus Proceratium in the extant and fossil record (Hymenoptera: Formicidae). Museo Regionale di Scienze Naturali, Monografie 36: 1-480.
  • CSIRO Collection
  • Hita Garcia F., E. M. Sarnat, and E. P. Economo. 2015. Revision of the ant genus ProceratiumRoger (Hymenoptera, Proceratiinae) in Fiji. ZooKeys 475: 97–112.
  • Liu C., G. Fischer, and E. P. Economo. 2015. A rare ant on Samoa: first record of the cryptic subfamily Proceratiinae (Hymenoptera, Formicidae) and description of a new Proceratium Roger species. Journal of Hymenoptera Research 46: 35-44.
  • Sarnat Eli M. 2009. The Ants [Hymenoptera: Formicdiae] of Fiji: Systematics, Biogeography and Conservation of an Island Arc Fauna. 80-252
  • Ward, Darren F. and James K. Wetterer. 2006. Checklist of the Ants of Fiji. Fiji Arthropods III 85: 23-47.