Camponotus senex

In Costa Rica, C. senex 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. Importantly, they never make silk nests among leaves. (Longino 2006)

Identification
Longino (2006) - The subgenus Myrmobrachys of Camponotus is characterized by workers with a somewhat box-like propodeum that has a broad, subrectangular dorsal face. Within this group there is a confusing set of morphologically similar species that vary in details of shape, surface sculpture, and pilosity. In Costa Rica extensive faunal inventory work has resulted in an improved understanding of species boundaries. The species I identify as C. senex is all black, the side of the mesosoma is densely punctate, there are abundant short erect setae projecting from the sides of the head in full face view, the mesosomal dorsum is abundantly setose, the gastral dorsum is abundantly setose with an underlying pubescence that is sparse. Some species, such as the common Camponotus planatus and the silk-making Camponotus textor, have dense appressed pubescence on the gaster that nearly obscures the underlying cuticle and gives the gaster a yellow to white color. In contrast, the black cuticle of C. senex is easily seen beneath the dilute pubescence and the gaster appears black. There is strong worker polymorphism: the major worker is relatively large compared to minor workers. This contrasts with C. textor, which has major workers that are little larger than minor workers.

Distribution based on Regional Taxon Lists
Neotropical Region: Brazil, Colombia, Costa Rica, Ecuador, Honduras, Mexico, Panama, Peru, Trinidad and Tobago.

Biology
De Oliveira et al. (2015), studying ant occupancy of Cecropia trees in southwest Bahia, Brazil, found three colonies of  opportunistically nesting in Cecropia pachystachya trees.

Nomenclature

 *  senex. Formica senex Smith, F. 1858b: 47 (w.q.) BRAZIL. Mayr, 1878: 868 (m.); Forel, 1879a: 96 (s.); Wheeler, G.C. & Wheeler, J. 1953e: 194 (l.). Combination in Camponotus: Mayr, 1862: 676; in C. (Myrmobrachys): Forel, 1912i: 91. Senior synonym of tomentosa: Emery, 1892b: 167. See also: Longino, 2006b: 133.
 * tomentosa. Tapinoma tomentosa Norton, 1868a: 60, pl. 2, fig. 2 (w.) MEXICO. Combination in Camponotus: Norton, 1868c: 3. Junior synonym of senex: Emery, 1892b: 167.

Longino (2006) - Camponotus senex was described in 1858 from material collected in Brazil. I have not made extensive examinations of C. senex from museum collections, but in my own collecting experience I have identified as C. senex material from Costa Rica, Panama, Venezuela, and Guyana. The range of the species based on published identifications is Mexico to Brazil. Alex Wild examined a syntype of C. senex and provided a high-resolution image. It differs from the Costa Rican material in having red instead of black legs, but this is a character that appears intraspecifically variable in many species of Camponotus. The syntype is also similar to a montane form of C. textor found in Costa Rica, and I cannot easily distinguish the two. However, the montane form of C. textor is more likely to be a local endemic species or geographic variant of C. textor. Type specimens from Brazil are more likely to be conspecific with the widespread generalized cavity nester that I recognize in Central America and northern South America.

Through an early misidentification by Forel, it has been thought that C. senex builds silk nests. There is no mention of the nest of C. senex in Smith's original description nor in Mayr's (1878) redescription. Forel (1879) reviewed the Camponotus species related to C. senex and identified a collection from Cordoba, Mexico, as C. senex. The Mexican collection was from a “paper nest among branches,” and Forel noted the similarity to the silk nests of Camponotus chartifex and Camponotus nitidior (subgenus Dendromyrmex). Forel (1899) described the subspecies C. senex textor, based on material that Tonduz collected in Costa Rica, from a carton nest on leaves. Forel later (1905) identified Brazilian material as C. senex and reported Göldi’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 C. senex with carton nests. This was followed by Wheeler and Wheeler (1953), Schremmer (1979), and Holldobler and Wilson (1983). The name C. senex should be disassociated from the silk-spinning Camponotus and C. textor applied instead.

Given the lack of dense gastral pubescence on C. senex, it is unlikely that Norton’s Camponotus tomentosa is actually a synonym of C. senex. However, given the unavailability of types for the old Norton names, it can rest in oblivion under C. senex.

Type Material
Longino (2006) - Syntype worker, queen: Brazil, RJ, Constancia (Rev. H. Clark) (image examined).