Cephalotes opacus

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Cephalotes opacus
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Cephalotes
Species: C. opacus
Binomial name
Cephalotes opacus
Santschi, 1920

Cephalotes opacus P casent0217839.jpg

Cephalotes opacus D casent0217839.jpg

Specimen Label


Little is known about the biology of Cephalotes opacus.


A member of the atratus clade appearing as sister species of Cephalotes placidus. Its main apomorphy, in the worker, are the short, cylindrical propodeal spines. (de Andrade and Baroni Urbani 1999)

Keys including this Species


Distribution based on Regional Taxon Lists

Neotropical Region: Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana (type locality), Peru, Suriname, Venezuela.

Distribution based on AntMaps


Distribution based on AntWeb specimens

Check data from AntWeb


The biology of many Cephalotes species is not known. Ants in this genus are common in the New World tropics and subtropics and are especially abundant and diverse in the canopies of Neotropical forests. The majority of species are arboreal. Species that live in other strata inhabit smaller trees, bushes or grass stems. These noon-arboreal species, due to their accessibility, are among the better studied members of the genus. There are also species that can be found in downed wood but it is likely the wood housed the colony before it fell to the ground. Soil nests are not known for any species nor do most species appear to extensively excavate plant tissue. They nest instead in preformed cavities. Overall, ants in the genus utilize a wide range of plants. Some species are predictable in their plant use but none appear to have evolved specialized mutualisms with particular plant species.

Worker castes typically include two forms, a worker and soldier, but there are a few species that are monomorphic. The larger soldier caste typically has an enlarged head disk. In some species the head of the soldier is very different from the worker while in others these differences are less pronounced. Queens and soldiers tend to share similar head morphology. Soldiers use their heads to plug the nest entrance. This can be very effective in excluding potential intruders. Other morphological differences between the worker castes are present but these differences have not been studied as well as head moprhology.

The behavioral repertoire of Cephalotes varians has been examined in great detail (ethograms from Wilson 1976, Cole 1980 and Cole 1983). Soldiers do little else besides defend the nest. This specialized soldier behavior is presumed to be the norm for most species. An especially interesting behavior occurs when workers are dislodged from trees: they "fly" towards the tree, often grabbing the trunk well above the ground (video).

Mature nest size varies, by species, from less than a hundred to many thousands of workers. Available evidence suggests most species are monogynous. Queens may mate with multiple males.

The proventriculus of the Cephalotes is peculiar relative to other ants. The morphology of the structure suggests it serves as a powerful pump and filter. This does not appear to lead these ants to have a highly specialized diet as most species appear to be general scavengers. Foragers have been observed feeding on carrion, bird feces, extrafloral nectaries and even tending membracids. Pollen feeding has been observed in some species, and this is somewhat specialized for ants, but it is not evident that any species restricts its diet to this resource in any significant way. Evidence for pollen feeding in Cephalotes has accumulated, in part, via finding digested pollen grains seen in infrabucal pellets. It has been suggested that the morphology of the proventriculus is a specialization for processing pollen.

More research examining all aspects of the biology of Cephalotes is needed. Our present understanding of these ants is largely based on species that live in locations other than the forest canopy, which is where Cephalotes are most common and diverse.



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

  • opacus. Cephalotes opacus Santschi, 1920f: 147 (w.) GUYANA. De Andrade & Baroni Urbani, 1999: 149 (q.m.). Combination in Eucryptocerus: Kempf, 1951: 131; in Cephalotes: De Andrade & Baroni Urbani, 1999: 147. Junior synonym of placidus: Kempf, 1959a: 92. Revived from synonymy and senior synonym of abdominalis: De Andrade & Baroni Urbani, 1999: 147.
  • abdominalis. Cephalotes abdominalis Santschi, 1929d: 302 (w.) FRENCH GUIANA. Combination in Eucryptocerus: Kempf, 1951: 129. Junior synonym of opacus: De Andrade & Baroni Urbani, 1999: 147.

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



de Andrade and Baroni Urbani (1999) - Head subquadrate. Border of the frontal carinae irregularly crenulate, with a small, median denticle. Eyes globose, behind of the scrobes. Vertexal angles with two pairs of teeth with lamellaceous border; the anterior tooth smaller and separate from the posterior one by a deep notch. Vertexal margin prolonged backwards into a visible neck. Vertex with a pair of denticles, more developed in larger specimens. Mandibles, laterally, with a superficially carinate tumulus.

Mesosoma. Anterior pronotal border with a superficial incision in the middle and with a developed scapular angle laterally. Anterior third of the pronotal sides straight, second third with a pair of long spines with bidenticulate tip, posterior third gently converging behind. Pronotal dorsum with a pair of denticles more developed in large specimens. Pronotal suture marked on the sides. Mesonotal sides unarmed, superficially marginate and gently converging posteriorly. Propodeal suture well impressed, less marked in the middle. Basal face of the propodeum with straight, weakly marginate sides and separate from the declivous one by a pair of cylindrical spines. Propodeal spines as long as half or less than half of the maximum length of the basal face of the propodeum. Declivous face of the propodeum straight and laterally separate from the broad metapleura by a carina.

Petiole subcylindrical, with truncate anterior face, dorsally and laterally unarmed and gently converging posteriorly. Postpetiole slightly higher than the petiole; anterior half of the postpetiolar sides convex or truncate, posterior half converging backwards.

Gaster with a pair of anterior lamellae or simply shortly marginate.

Legs. Mid and hind femora without angle or denticle medially but with a pair of faint longitudinal carinae on the two posterior thirds. Hind basitarsi long, laterally compressed and slightly broadening at the base.

Sculpture. Head entirely minutely and superficially reticulate and with foveae diminishing in size anteriorly, denser on the on their posterior third, very superficial on the frons and on the hypostomal area of some specimens. Mesonotum minutely reticulate and with variably distributed and impressed foveae; in some specimens the foveae are smaller, sparser and more superficial on the mesonotum and on the propodeum. Pedicel minutely reticulate and with dense, mall foveae. Gaster and legs reticulate. Femora with thin, short, irregular, superficial rugosities. Centre of the first gastral tergite and sternite superficially reticulate and shining.

Pilosity. Each fovea with a thin, short, appressed, pointed hair; similar hairs but not originating from the foveae on the legs and on the gaster. Anterior border of the frontal carinae, vertexal angles, pronotal spines and legs with rare, short, suberect, clavate hairs; similar hairs but longer and slender on the legs and on the posterior border of the gastral tergites and sternites. Sternites with long, pointed hairs.

Colour. Black and variably opaque. Frontal carinae with two pairs of infuscate dark-reddish, opaque maculae. Border of the vertexal angles, of the gastral lamellae and tarsomeres dark-ferrugineous.

Measurements (in mm) and indices: TL 6.56-8.70; HL 1.54-2.40; HW 1.94-2.40; EL 0.40-0.48; PW 1.68-2.28; PeW 0.50-0.62; PpW 0.52-0.60; HBaL 0.96-1.20; HBaW 0.19-0.25; CI 115.6-125.9; PI 104.0-115.5; PPeI 336.0-392.8; PPpI 297.1-340.3; HBaI 19.8-21.4.


de Andrade and Baroni Urbani (1999) - Differing from the worker for the following characters: frontal carinae gently converging in front of the eyes. Vertexal teeth smaller and without lamellaceous border. Vertex with a pair of larger denticles. Eyes less globose.

Mesosoma. Notch on the anterior pronotal border almost absent. Pronotal sides with thicker and shorter spines. Pronotal dorsum with a pair of broad, flat, triangular teeth. Mesonotal sides unarmed or slightly convex, superficially marginate and gently converging posteriorly. Propodeal suture deeply impressed.

Gaster with a pair of lamellae of variable size.

Measurements (in mm) and indices: TL 10.32-10.60; HL 2.40-2.48; HW 3.00; EL 0.56-0.60; PW 2.84-2.96; PeW 0.72-0.76; PpW 0.80-0.84; HBaL 1.24-1.32; HBaW 0.28; CI 121.0-125.0; PI 101.3-105.6; PPeI 373.7-411.1; PPpI 352.4-355.0; HBaI 21.2-22.6.


de Andrade and Baroni Urbani (1999) - Head subquadrate, slightly broader than long and with subparallcl sides. Frons gently convex. Frontal carinae converging anteriorly and straight up to the vertexal angles. Frontal carinae broadly crenulate and with a small tooth in the middle. Vertexal angles with a pair of small teeth separate by a concavity from a low, anterior angle, the angle round and poorly projecting. Vertex marked by a pair of triangular teeth. Mandibles as in oculatus.

Mesosoma. Humeral angles bearing a thick, pointed tooth. Pronotal crest well marked, high, with crenulations and interrupted in the middle by a superficial impression. Mesonotum, scutellum, lower mesopleurae and sides of the declivous face of the propodeum as in oculatus. Basal face of the propodeum much lower than the scutellum and short; its sides with a pair of subtriangular spines, slightly diverging backwards.

Petiole with differentiate anterior and posterior faces; anterior face truncate, posterior face gently sloping posteriorly. Petiole unarmed and with the sides weakly converging posteriorly. Postpetiole convex dorsally; sides of the postpetiole slightly convex

Gaster with a thin lateral margin not surpassing the first gastral stigma posteriorly.

Legs as in oculatus.

Sculpture as in oculatus differing only in the size of the foveae, generally larger and sparser on the lower mesopleurae.

Pilosity as in oculatus.

Colour. Black. Tarsomeres brown.

Measurements (in mm) and indices: TL 14.52; HL 2.64; HW 3.04; EL 0.64; PW 3.24; PeW 0.96; PpW 1.08; HBaL 1.44; HBaW 0.31; CI 115.1; PI 93.8; PPeI 337.5; PPpI 300.0; HBaI 21.5.


de Andrade and Baroni Urbani (1999) - Head (eyes included) slightly less than 1/3 broader than long. Vertexal angles, medially, with a broad, triangular denticle continuing into a longitudinal, incomplete carina almost reaching the internal border of the eye. Vertexal margin prolonging backwards into a broad neck. Vertex dorsally gently convex and bearing salient ocelli. Compound eyes convex, in the middle of the sides of the head. Frontal carinae high, slightly convex, broad, not reaching the impair ocellus but diverging backwards into a thin, irregular margin. Frons flat posteriorly, slightly declivous anteriorly. Clypeus convex posteriorly and with almost truncate anterior face. Mandibles slim, laterally with a superficial carina. Scapes thick and short, not reaching the posterior border of the eyes. Funiculi thickening from the base to the apex.

Mesosoma. Pronotum in dorsal view with the sides diverging backwards. Mesonotum convex in side view; only pair Mayrian furrows impressed and visible. Scutellum convex and higher than the mesonotum, its sides converging posteriorly. Basal face of the propodeum much lower than the scutellum; dorsum of the basal face sloping backwards, but differentiate from the declivous one; sides of the basal face gently converging backwards, with the posterior half bearing a short, carinate, triangular tooth. Declivous face laterally marked by a pair of longitudinal, convergent carinae.

Petiole and postpetiole cylindrical; anterior petiolar face truncate and dorsally carinate.

Gaster very narrow and elongate; the first segment ca. 1.5 times longer than broad.

Sculpture. Head dorsum minutely reticulate and with sparse, irregular, thin rugosities; vertexal angles with irregular foveae; frons with very superficial foveae, small foveae. Ventral part of the head with the same type of sculpture as on the vertexal angles, the foveae diminishing in size and more superficial on the anterior part. Pronotum, mesonotum and scutellum reticulate and with sparse, irregular foveae; the same sculpture but separated by short, irregular rugosities on the basal face of the propodeum, on the anterior half of the petiole and on the sides of the postpetiole. Pedicel, pleurae, declivous face of the propodeum and first gastral tergite deeply reticulate; the reticulation less impressed and more shining on the remaining tergites, on the sternites and on the legs.

Pilosity. Body with three types of hairs: (1) suberect, long hairs, more dense on the head, on the mesosoma and on the apex of the gaster, sparse on the pedicel and on the legs, shorter on the first sternite; (2) short, sparse, appressed on the legs and on the gaster, rare on the pedicel; (3) similar to type (2) but longer, thicker and dense on the internal, anterior and posterior faces of the tibiae and on the tarsomeres.

Colour. Head, mesosoma and pedicel opaque black. Two anterior thirds of the first gastral tergite dark reddish brown. Remaining tergites, sternites and legs ferrugineous and slightly shining.

Measurements (in mm) and indices: TL 8.80; HL 1.36; HW 1.48; EL 0.51; PW 1.24; PeW 0.65; PpW 0.70; HBaL 1.16; HBaW 0.16; CI 108.8; PI 119.3; PPcI 190.8; PPpI 177.1; HBal 13.8.

Type Material

de Andrade and Baroni Urbani (1999):

Worker. Type locality: St. Jean du Maroni (French Guyana). Type material: holotype worker (unique), without head in Naturhistorisches Museum, Basel (examined).

Cephalotes abdominalis Worker. Type locality: St. Jean du Maroni (French Guyana). Type material: lost; the original pin is still in the Naturhistorisches Museum, Basel but no ant is glued to the label nor can it be found in the drawer.


  • de Andrade, M. L.; Baroni Urbani, C. 1999. Diversity and adaptation in the ant genus Cephalotes, past and present. Stuttgarter Beitrage zur Naturkunde Series B (Geolgie and Palaontologie). 271:1-889. (page 149, queen, male described, page 147, Combination in Cephalotes, Revived from synonymy and senior synonym of abdominalis)
  • Kempf, W. W. 1951. A taxonomic study on the ant tribe Cephalotini (Hymenoptera: Formicidae). Rev. Entomol. (Rio J.) 22: 1-244 (page 131, Combination in Eucryptocerus)
  • Kempf, W. W. 1959a. Sôbre algumas formigas Cephalotini do Museu de Oxford (Hymenoptera, Formicidae). Rev. Bras. Biol. 19: 91-98 (page 92, Junior synonym of placidus)
  • Santschi, F. 1920f. Nouvelles fourmis du genre Cephalotes Latr. Bull. Soc. Entomol. Fr. 1920: 147-149 (page 147, worker described)