Wasmannia auropunctata (Roger)

Longino, J. T. & Fernández, F., 2007, Taxonomic review of the genus Wasmannia., Advances in ant systematics (Hymenoptera: Formicidae): Homage to E. O. Wilson - 50 years of contributions. (Memoirs of the American Entomological Institute 80), pp. 271-289 : 276-278

Wasmannia auropunctata (Roger)

Tetramorium auropunctatum Roger, 1863: 182. Syntype worker, queen, male: Cuba (not examined). Combination in Ochetomyrmex : Forel, 1886; in Wasmannia : Forel, 1893.

Description of larva: Wheeler, G. C. & Wheeler, J., 1954: 444.

Ochetomyrmex auropunctatus var. rugosus Forel , 1886: xlix. Syntype worker: Guatemala, Retalhuleu (Stoll) [ MHNG] (examined). Combination in Wasmannia : Forel, 1901: 128 .

Description of queen, male: Santschi, 1929: 299. NEW SYNONYMY.

Wasmannia auropunctata var. australis Emery , 1894: 193. Syntype worker: Brazil, Rio Grande do Sul (v. Ihering ). NEW SYNONYMY .

Wasmannia auropunctata var. laevifrons Emery , 1894: 193. Syntype worker: Bolivia, Coroico, Chulumani Yungas (Balzan). NEW SYNONYMY.

Wasmannia auropunctata var. nigricans Emery , 1906: 160. Syntype worker: Paraguay, Tacuru Pucu. NEW SYNONYMY.

Wasmannia auropunctata var. obscura Forel , 1912: 1. Syntype worker: Dibulla , Burithaka and Don Diego , Sierra Nevada de Santa Marta, Colombia (Forel); Ceara, Brazil (Diaz da Rocha) ; Santos , Brazil (Dr. Ris) [ MHNG] (Dibulla and Ceara syntypes examined, Ceara worker here designated LECTOTYPE). NEW SYNONYMY.

Xiphomyrmex atomum Santschi, 1914: 370. Syntype worker: Gabon, Libreville (Silvestri) [ NHMB] (examined). Combination in Wasmannia , and variety of auropunctata : Santschi, 1916: 504. Junior synonym of auropunctata : Wheeler, 1922: 912 .

Wasmannia glabra Santschi , 1931: 272. Syntype queen: French Guiana, St. Laurent du Moroni (Le Moult) [ NHMB] (examined). Junior synonym of auropunctata : Kempf, 1964: 66 .

Wasmannia auropunctata st. pulla Santschi , 1931: 272. Syntype worker: Panama, France Field , 9 May 1930 (A. Bierig) [ NHMB] (examined). NEW SYNONYMY .

Hercynia panamana Enzmann, J. 1947: 44, pl. 5. Syntype worker, queen: Panama. Junior synonym of auropunctata : Brown, 1948: 102.

Taxonomic comments

Workers of W. auropunctata have a strongly quadrate petiolar node. The anterior face of the node is sharply differentiated from both the peduncle and the dorsal face of the node, meeting both at nearly right angles, and forming a strongly step-like profile. This is a highly distinctive feature that easily distinguishes auropunctata workers from all other Wasmannia species. Within the species there is abundant variation in the strength of sculpturing and coloration, and this has engendered the naming of nine infraspecific forms in addition to the nominotypical. We have never been able to discover evidence of discrete forms among the workers of auropunctata , either in sympatry or allopatry; the variation appears continuous. Three of the forms have already been synonymized by others: atomum , glabra , and panamana . We have been able to examine types of three additional forms — obscura , pulla , and rugosa — and they fall well within our concept of auropunctata . The remaining forms — australis , laevifrons , nigricans — we have not examined, but the published descriptions give no indication that they are beyond the range of variation of auropunctata . We have synonymized them, following the philosophy that taxa should be synonymized unless evidence of distinctness is obtained.

The above synonymy does not assure that there is no genetic structuring, and perhaps species-level differences, within the broad concept of auropunctata . There may even be distinct sympatric species. In Costa Rica, there appear to be two size classes of queens (Fig. 2). Queens with smaller heads include ten from various sites in Costa Rica, including La Selva Biological Station and the Penas Blancas Valley, one from Jamaica, and one from Venezuela. Queens with large heads are all from the Atlantic slope of Costa Rica. Three are from La Selva (two from different Winkler samples of sifted leaf litter from the forest floor, one from a small nest under an epiphyte mat in an old treefall) and one is an alate queen found in a Cecropia sapling near Volcan Arenal. Thus the small-headed and big-headed forms are broadly sympatric in Costa Rica. Among the small-headed queens four are definitively associated with workers from the same colony, and among the big-headed queens one is associated with workers. Others have workers doubtfully associated (together in the same Winkler sample). We can discern no differences in workers associated with the two types of queens. The cause of the two size classes of queens is unknown, but could reflect either differences between cryptic species or intraspecific polymorphism.

An aberrant worker form is frequently encountered in large samples of W. auropunctata . These aberrant workers have the head grossly swollen. The entire head is more spherical than normal, as if the head were inflated like a balloon. The rest of the body is little different from a normal worker. These aberrant workers are occasionally encountered in Winkler samples that contain hundreds or thousands of auropunctata workers.

Natural History

Wasmannia auropunctata is a widespread pest ant (Clark et al., 1982; De Souza et al., 1998; Fabres & Brown, 1978; Jourdan, 1997; Lubin, 1984; Ulloa Chacon & Cherix, 1990; Williams, 1994; Wetterer & Porter, 2003). In its presumed native range it occurs from Argentina to Mexico (Kempf, 1972; Wetterer & Porter, 2003). Its introduced range includes the Galapagos Islands, West Africa (Gabon, Cameroon, and possibly the Republic of Congo and the Democratic RepubIic of Congo), Melanesia (New Caledonia, Solomon Islands, Vanuatu, and possibly Tuvalu), Polynesia (Wallis and Futuna and Hawaii), parts of the US (Florida and possibly California), and subtropical Atlantic islands (the Bahamas and Bermuda) (Wetterer & Porter, 2003). It is widespread on Caribbean islands, but it is unclear whether these are long-term native populations or recent introductions (Wetterer & Porter, 2003).

The species is remarkably catholic in its habitat preference. It is common in habitats ranging from wet to dry and from early successional to mature. In an elevational gradient of mature wet forest on the Atlantic slope of Costa Rica (the Barva Transect, from La Selva Biological Station to 2000 m elevation on the slope of Volcan Barva) it is abundant at 50 m and 500 m elevations, but nearly absent at 1070 m (Table 2). In the lowland habitats where it is abundant, it occurs in leaf litter on the forest floor and at all levels in the vegetation.

Although it occurs frequently in samples from mature forest habitats in Costa Rica, it is never so abundant in those habitats that it is noticeable as a pest or appears to be displacing other native species (Tennant, 1994; McGlynn & Kirksey, 2000; pers. obs.). In contrast, in certain agricultural habitats (banana plantations) and in parts of the tropics where it has been introduced it becomes super-abundant, with negative impacts on native species and human comfort (Clark et al., 1982; Wetterer & Porter, 2003). In dry-forest fragments in Colombia there is a negative correlation between W. auropunctata abundance and overall ant diversity (Armbrecht & Ulloa Chacon, 2003). Where introduced in New Caledonia it invades dense native forest and displaces native ants (Le Breton et al., 2003). Behavioral tests and cuticular hydrocarbon analysis show that W. auropunctata is multicolonial in its native range in Brazil, unicolonial where introduced in New Caledonia (Errard et al., 2002).

The sting of Wasmannia is noteworthy. These are extremely tiny ants, barely visible in the field. When the senior author first began studying ants in Costa Rica, he was at first puzzled about Wasmannia . By literature accounts Wasmannia was reputed to have a terrible sting, but he had been collecting them for months in Corcovado National Park without ever experiencing the famous sting. One day he was collecting from a populous nest and some workers made it up to the soft skin of his inner forearm and began to sting. The sting was definitely noticeable, about as severe as a fire ant (i. e., Solenopsis geminata ) but inordinately strong for an ant that could barely be seen! Workers are so small they cannot sting through the thicker skin of the hands.

Surprisingly, the chemical and toxicological nature of the venom of W. auropunctata has not been investigated. Howard et al. (1982) discovered an alkylpyrazine compound in the mandibular glands, which acted as an attractant to conspecifics and a repellent to heterospecifics. They speculated that the workers might apply the mandibular gland product as an irritating secretion, augmenting the defensive properties of the venomous sting. It would be interesting to investigate whether the venom alone is the powerful agent in this small ant, or if the strong burning sensation is a synergetic effect of venom plus mandibular gland product.

Nests can be almost anywhere: in rolled leaves or dead sticks in the leaf litter, under stones, in rotten wood, in hollow stems suspended above the ground, in ant-plant domatia, and under epiphytes. Workers are omnivorous scavengers and predators and can rapidly recruit to food. Colonies are polygynous and it is never clear where colony boundaries are. Dozens of dealate queens may be found together in nests. Males are rare but do occasionally occur.