Formicinae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
Minor worker, dorsal view (reduced, original).
Collection from Osa Peninsula, minor worker, lateral view (reduced, original); face view (reduced, original); dorsal view of gaster (reduced, original); major worker, lateral view (reduced, original); face view (reduced, original).
Mexico to southern Brazil. Costa Rica: Atlantic and southern Pacific lowlands, Central Valley.
Minor worker: Propodeum lacking spines or tubercles of any kind; propodeum somewhat box-like, dorsal and lateral faces flat or nearly flat and meeting at an approximate right angle; dorsal face of propodeum subrectangular; pubescence on first gastral tergite dilute, appressed to suberect, not obscuring integument; color black; propodeum not strongly projecting, forming part of continuous dorsal profile of mesosoma; in face view with relatively abundant erect setae projecting from sides of head, from mandibular insertions to level of eyes; erect setae on first gastral tergite relatively short (longer on JTL-045 and brevis).
Similar species: planatus, JTL-045, brevis, textor.
This species is very common in lowland wet forest habitats. It can occur in both mature forest and highly disturbed areas. For example, workers are very common in canopy fogging samples from mature forest at La Selva Biological Station, yet I have also found them on the landscaping around the Juan Santa Maria airport near San Jose. Foragers are diurnal.
Nests occur in highly insolated areas such as upper forest canopy, open scrubby or second growth vegetation, roadsides, and agricultural land. The species is an opportunistic cavity nester. Nests are in dead branches, ranging from narrow vine stems to relatively large branches. In surveys of Cecropia trees, I often find nests in internodes of saplings, or in mature trees abandoned by Azteca, or in peripheral portions of trees that have a dominant Azteca colony elsewhere in the crown.
This species is morphologically and behaviorly very similar to C. planatus. The two species seem to differ in the degree of habitat disturbance they prefer. This species is relatively more common in mature forest habitats, while C. planatus dominates in open areas subject to higher disturbance rates.
Through an early misidentification by Forel, it has been thought that senex builds silk nests. There is no mention of the nest of senex in Smith's original description nor in Mayr's (1878) redescription. Forel (1879) reviewed the Camponotus species related to senex, and identified a collection from Cordoba, Mexico, as senex. The Mexican collection was from a "paper nest among branches," and Forel noted the similarity of the nest of "senex" with the silk nests of chartifex and nitidior (subgenus Dendromyrmex). Forel (1899) described the subspecies textor, based on material that Tonduz collected in Costa Rica, from a carton nest on leaves. Forel later (1905) identified Brazilian material as senex and reported Gldi's observations that the larvae are used to spin silk for the nest. Wheeler (1915) reviewed use of larval silk for nest construction by ants, perpetuating the association of senex with carton nests. This was followed by Wheeler and Wheeler (1953), Hlldobler and Wilson (1983), and Schremmer (1979).
Alex Wild provided an image of the type of senex (Click here) and it is clearly not the Costa Rican species that builds silk nests. All the observations of "Camponotus senex" using larvae to make exposed silk nests are of other species that are not senex. See textor.
Forel, A. 1879. tudes myrmcologiques en 1879 (deuxime partie [1re partie en 1878]). Bull. Soc. Vaudoise Sci. Nat. 16:53-128.
Forel, A. 1899. Biologia Centrali-Americana; or, contributions to the knowledge of the fauna and flora of Mexico and Central America. Insecta. Hymenoptera. 3 (Formicidae). London. 169 pp.
Forel, A. 1905. Einige biologische Beobachtungen des Herrn Prof. Dr. E. Gldi an brasilianischen Ameisen. Biol. Centralbl. 25:170-181.
Holldobler, B., and E. O. Wilson. 1983. The evolution of communal nest-weaving in ants. American Scientist 71:490-499.
Mayr, G. 1878 ("1877"). Formiciden gesammelt in Brasilien von Professor Trail. Verh. K-K. Zool.-Bot. Ges. Wien 27:867-878.
Schremmer, F. 1979. Das Nest der neotropischen Weberameise Camponotus (Myrmobrachys) senex Smith (Hymenoptera, Formicidae). Zoologischer Anzeiger 203:273-282.
Smith, F. 1858. Catalogue of hymenopterous insects in the collection of the British Museum. Part VI. Formicidae. London: British Museum, 216 pp.
Wheeler, G. C., Wheeler, J. 1953. The ant larvae of the subfamily Formicinae. Ann. Entomol. Soc. Am. 46:126-171.
Wheeler, W. M. 1915. On the presence and absence of cocoons among ants, the nest-spinning habits of the larvae and the significance of black cocoons among certain Australian species. Ann. Entomol. Soc. Am. 8:323-342.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.firstname.lastname@example.org
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