Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Identification
constructor is an obligate Cecropia ant (Longino 1989, 1991a,b).
Worker: scapes and tibiae with abundant, conspicuous setae; strongly polymorphic, largest worker HW approaching 1.40mm. In Costa Rica, workers of constructor are very difficult to distinguish from workers of xanthochroa. In constructor, the largest workers are uniform brown, and the head is more quadrate. In xanthochroa, the largest workers approach the queen in color, with the sides of head orange, and the sides of the head are more rounded (figure). At some upland wet forest sites in Costa Rica, where A. xanthochroa colonies appear somewhat stunted, worker series of A. xanthochroa and A. constructor are nearly indistinguishable.
Queen: scapes and tibiae with abundant, conspicuous setae; color black; mesosoma and face with dense brush of setae, continuous from ocelli to occipital lobes and on anteriormost mesoscutum; average height of setal brush (perpendicular to surface) on both face and mesoscutum greater than 0.30mm.
Colonies of xanthochroa and constructor are relatively easy to distinguish in the field because of difference in nest structure. xanthochroa usually maintains a vertical fissure near the base of the tree, and does not have entrances near the central nest. constructor does not maintain a fissure near the base of the tree, but rather has multiple fissures near the nest. See additional details under Natural History.
Range
Guatemala south through lower Central America, coastal lowlands of northern South America eastward to Guyana.
Natural History
See also general treatment of the Cecropia-Azteca association in Costa Rica.
constructor occurs throughout Costa Rica, in a wide variety of habitats and in a variety of Cecropia species. I have found queens in Cecropia saplings from sea level to 1500m. Queens occur abundantly in saplings of C. peltata, C. obtusifolia, and C. insignis, and I have occasionally found queens in saplings of C. angustifolia, a non-myrmecophytic cloud forest species which does not harbor Azteca colonies when mature. In the lowlands, A. constructor colonies are common in mature trees of C. peltata on the Pacific coast and C. obtusifolia on the Atlantic coast. In the Atlantic lowlands, mature C. insignis trees are dominated by A. ovaticeps (D. and D. Clark, pers. com., and pers. obs.). This contrasts with the uplands, where in relatively undisturbed forest C. insignis is the only myrmecophytic Cecropia species. In these upland sites, saplings are filled with queens of A. constructor and A. xanthochroa, which implies that nearby mature trees of C. insignis must harbor reproductive colonies of A. constructor. Thus, hostplant use appears to vary with region and elevation.
Pleometrosis at colony founding is very common, particularly at upland sites, and I have found up to 10 queens in a single internode. Mixed-species associations are common, with queens of A. constructor and A. xanthochroa inhabiting the same internode. Colonies at a stage where there are hundreds of workers and the queen has become physogastric are generally monogynous, but I have twice observed colonies at this stage with two physogastric queens. In both cases, the queens have been close together in the central carton nest of the colony. Multiple physogastric queens in young colonies are apparently common in Monteverde, Costa Rica (D. Perlman, pers. com.). I have dissected two mature colonies of A. constructor, and both were monogynous.
Mature colonies occupy a single carton nest in the bole of the tree. The nest is spindle-shaped and causes a deformation of the trunk. All larvae and alate sexuals are concentrated in this single nest. Branchtips, which all communicate internally with the carton nest, contain only workers and Homoptera. Workers of this species are extremely aggressive, and respond to any disturbance by pouring out of large fissures near the carton nest and blackening the trunk surface.
Literature Cited
Longino, J. T. 1989. Geographic variation and community structure in an ant-plant mutualism: Azteca and Cecropia in Costa Rica. Biotropica 21:126-132.
Longino, J. T. 1991a. Azteca ants in Cecropia trees: taxonomy, colony structure, and behavior. Pages 271-288 in C. Huxley and D. Cutler, editors. Ant-plant interactions. Oxford University Press, Oxford, U.K.
Longino, J. T. 1991b. Taxonomy of the Cecropia-inhabiting Azteca ants. Journal of Natural History 25:1571-1602.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. longinoj@evergreen.edu
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