Karavaievia

This is currently a subgenus of Camponotus. Please see Camponotus for further information.

Biology
Dumpert et al. (2006) - Natural preformed nesting sites are rather limited in the canopy region of the tropical rainforest. By constructing free-hanging nests in this habitat, weaver ants get access to the leaf and crown region. In these ants silk of the larval labial glands is not only used by the mature larvae themselves for spinning their pupal cocoon but also for nest construction. Like weaver shuttles worker ants take large larvae with their mandibles and use the silk secreted by them to spin together leaves or to form flexible and firm carton nest walls out of particles with help of the fresh sticky silk.

Until recently four independent groups of weaver ants were known worldwide, all of them belonging to the subfamily Formicinae. Two are found in the Old World tropics (the famous genus Oecophylla Smith, 1860 and many species of the genus Polyrhachis Smith, 1857) and two in the New World tropics (species of the subgenera Dendromyrmex Emery, 1895 and Myrmobrachys Forel, 1912 of Camponotus Mayr, 1861) (Hölldobler & Wilson 1977, Schremmer 1979).

In 1984 we discovered in Peninsular Malaysia near the Ulu Gombak Field Studies Centre of the University of Malaya an Old World silk-weaving Camponotus species which produces silk carton nests mainly beneath leaves of trees containing brood as well as trophobiotic hemipteran symbionts. This hitherto unknown species turned out to belong to the subgenus Karavaievia.

Life conditions and geographic distribution of Karavaievia
Dumpert et al. (2006) - In the evergreen rainforest zone of Southeast Asia most of the woody plants possess leaves that persist over several years and are not shed synchronously (Whitmore 1988). Only this type of leaf is suited as a substrate for the long-lasting nest pavilions built by Karavaievia. All known Karavaievia species nest in this way. Moreover Karavaievia workers are able to recognize in advance the moment of natural shedding of inividual leaves, possibly through the change of honey dew production of their trophobionts on the decaying leaves within the pavilions (Waldkircher and Maschwitz 2002). Consequently, without any loss of colony members such pavilions can be abandoned in time and their brood and trophobionts can be transported to other leaf nests before leaf drop. Synchronous annual defoliation, however, as commonly occurring in woody plants of the monsoon zone during the dry season would simultaneously destroy the numerous pavilions of a Karavaievia colony on such a plant, i.e., its whole nesting and trophic base.

Correspondingly, most, i.e., 15 of the known 18 Karavaievia species were found in the evergreen rainforest region of Sundaland, i.e., Borneo, Peninsular Malaysia, Sumatra and Mentawei island (Dumpert et al. 1995). Many of these have been found only once or twice. Only Karavaievia texens was found frequently, within a large area ranging from the east coast of Peninsular Malaysia to West Sumatra (Dumpert et al. 1995 and unpubl.). We suppose that many more species remain undiscovered in the vast unexplored regions of ever wet Sundaland: no collections exist from the moist regions of Java, from large parts of Borneo and Sumatra and from many smaller islands. As Karavaievia is neither specialized in living on specific plant species nor in cultivating specific trophobionts and as colony founding queens are able to disperse over water by flight, no limitations by the classical biogeographic Sundaland distribution borders, e.g., such as Wallace's Line, have to be expected (Whitmore 1988). Thus Karavaievia should also be looked for on Sulawesi and on the Philippines.

Colony foundation, rareness and high species diversity in Karavaievia
Dumpert et al. (2006) - Most species of Karavaievia have only been collected once or twice indicating their rareness in their habitats. The supposition that colonies are abundant in the inaccessible upper forest canopy is not consistent with our long term observations. We often have found their colonies in lower and middle heights of the forest. Additionally the crowns of hundreds of larger fallen trees checked over many years in our observation area in the Gombak valley/Peninsular Malaysia never were inhabited by any Karavaievia colonies. Here in a quantitative counting during a road side clearing action 312 fallen trees up to 12 m height were checked for ants: 12 % of them were occupied by weaver ants (Oecophylla or Polyrhachis spp.) and 6 % contained carton nests of various ants, but none was inhabited by any Karavaievia. During extensive research on nest building behavior, nest architecture and details of nest materials (silk, diverse plant material [carton-nest], and minerals), in tropical canopy-dwelling Formicidae we found clear indication not only for genus specific but even species specific nest constructions (Weissflog 2001). Thus, the majority of free-hanging canopy nests can be assigned to species even without seeing the original inhabitants. An important reason for the rareness might be the mode of colony foundation of Karavaievia species as described here. The typical mode of colony foundation in Karavaievia seems haplometrotic (a single queen establishes a new colony). Because colony-founding queens are not able to build pavilions without silk of last stage larvae, they cannot form any foundation pavilions under free hanging plant leaves. Instead, in at least two species, such queens used as foundation chambers abandoned or weakly colonized leaf nests of other pavilion building canopy ants which still contained trophobionts. We found colony founding queens of Karavaievia in nests of Monomorium species (Myrmicinae) which are able to construct their leaf pavilions without silk. This hitherto unknown mode of colony foundation has been found so far in C. (K.) schoedli from Thailand and in C. melanus from Borneo. In the cases of Camponotus schoedli and Camponotus melanus the colony founding queen was detected with her own brood and trophobiotic partners inside a single Monomorium sp. nest pavilion, while workers of Monomorium nested in the neighborhood on the same tree in separate pavilions.

A large colony of Camponotus micragyne from Sumatra mainly inhabited species specific self-constructed pavilions. However, it also had fully taken over some of the typical pavilions of a canopy dwelling Monomorium. Some Monomorium sp. pavilions were inhabited by C. micragyne and by Monomorium sp. at the same time.

This observation indicates that also in this species colony foundation may happen in a similar way to that of C. schoedli and C. melanus.

A similar mode of colony foundation is known from one type of true social parasites, the “temporary social parasites”. They have developed a high species diversity in temperate zones but are lacking in the tropics. Like Karavaievia, they are rare compared to their host species. Like Karavaievia temporary social parasites penetrate into the colonies of their hosts. However true social parasites are different in that they take over not only the nest building but also workers and brood of the host ant colony after having killed its queen. Phylogenetically, true social parasites appear to have evolved directly from their host species or from closely related ancestors. This is the so-called “Emery's Rule” (Emery 1909).

We do not know whether the Karavaievia queens kill the Monomorium sp. individuals during the take-over of the Monomorium nest pavilions. Nevertheless such a take-over can be classified as a mild sort of interspecific parasitism. However, we do not know whether Karavaievia also take over abandoned pavilions of Monomorium sp. or nests of other pavilion building canopy ants. Thus questions about whether these relationships are obligate or facultative and whether it is specific or non specific nest founding parasitism, remain open. At present, we can only suppose that the take over of trophobionts is obligate.

More common SE Asian canopy weaver ants like Oecophylla smaragdina (Fabricius, 1775) or various Polyrhachis species need no preformed pavilions and no trophobionts for colony foundation (Dorow and Maschwitz 1990, Liefke et al. 1998, Buschinger 2001, Weissflog 2001).

Nomenclature

 *  KARAVAIEVIA [subgenus of Camponotus]
 * Karavaievia Emery, 1925b: 115 [as subgenus of Camponotus]. Type-species: Camponotus exsectus, by original designation.