Dolichoderinae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Images of worker (click here)
Images of male (click here)
Images of queen: face view (small file, large file); lateral view (small file, large file)
Images of queen forewing and worker brood (click here)
Range
Costa Rica: Atlantic and Pacific slopes.
Identification
There is only one species in the genus known from the Americas. Similar dolichoderine genera in Costa Rica are Azteca and Tapinoma. Workers of Bothriomyrmex can be distinguished from Azteca by the shape of the propodeum. The dorsal face is much shorter than the posterior face, giving the mesosoma a compact appearance; in Azteca the dorsal face is longer than the posterior face and the mesosoma appears more elongate. Bothriomyrmex differs from Tapinoma in having a distinct, scale-like petiolar node. In the field, workers are superficially similar to some Brachymyrmex.
Natural History
This is the first report of this genus in the Americas, and it is now known from two separate collections from widely separated localities.
The first collection was made in February 2003, during the Project ALAS expeditions to the 500m site on the Volcan Barva transect (locality: Costa Rica, Prov. Heredia, 10km SE La Virgen, 10deg20'N 85deg04'W, 500m). The expeditions were based at the "El Ceibo" guard station, on the west bank of the Rio Peje. The station building itself is in pasture abutting mature rainforest. A few meters inside the forest a large tree had fallen sometime during the months prior to the expeditions. A few of the tree's leaves were still green; most were brown but still attached to branches. There were still extensive epiphyte mats covering the trunk and major branches. I collected from beneath these mats and found Bothriomyrmex workers and brood piles to be abundant beneath most of the mats. Large Margarodidae were also scattered amongst the Bothriomyrmex. Other ant species occurred under the mats and were somewhat interdigitated with the Bothriomyrmex, although much less abundant. These included Hypoponera opacior, a small yellow Solenopsis, and Tapinoma. Smaller nests or aggregations were also found of Crematogaster sotobosque and Pheidole biconstricta. One part of the tree, near the pasture edge, was being invaded by Solenopsis geminata. I found only workers and brood. Ronald Vargas of Project ALAS collected more from the same tree in April. His collections included two adult males.
Also in February of 2003 John Noyes of the British Museum was working in Costa Rica. He was taking large sweep samples from vegetation at several localities and extracting Encyrtidae, his primary focal taxon. He also separated ants and sent these samples to me, requesting a rough count of the number of ant species in each sample. Each sample contained hundreds to thousands of ants, including many alates. In the sample from Estacion Cacao (locality: Costa Rica, Prov. Guanacaste, Guanacaste Conservation Area, Estacion Cacao, 10deg55'N 85deg30'W, 1100m) I was surprised to find about a dozen males and a similar number of dealate queens of Bothriomyrmex! The habitat at Est. Cacao is a mosaic of mature montane moist forest with epiphyte-laden trees and abandoned pastures. This is a site on the Pacific slope of the northernmost cordillera in Costa Rica, 170km from the El Ceibo site on the Atlantic slope.
It was a great surprise to have two different collections taken at widely separated sites at more or less the same time. This suggests the species is relatively common in Costa Rica. Yet it has never been collected before, in spite of over a century of intensive ant collecting by many researchers. One possibility is that the species is recently introduced and has been quietly and rapidly spreading, and it is capable of invading mature forest habitats. The second possibility is that the species is so small and nondescript in all castes that it has simply been overlooked, and a fortuitous sequence of events resulted in the simultaneous occurrence of two collections. First, workers that live beneath epiphyte mats are not easily sampled by common methods such as baiting or canopy fogging. Second, my increasing nearsightedness has resulted in a slower collecting style that involves getting my nose very close to the substrate, and I can more easily see very small ants. Third, ant collectors rarely take or examine sweep samples, especially those taken by an encyrtid taxonomist dedicated to finding small Hymenoptera. When such samples are examined, often the emphasis is on workers and sexuals are ignored. Finally, having just discovered workers and males of Bothriomyrmex, I was primed to notice the males and diminutive queens in the sweep samples. Perhaps, like a new word one learns, I will start seeing them everywhere now.
Other species, and perhaps the genus as a whole, are temporary social parasites of the genus Tapinoma (see Genus Overview).
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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