Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
Southern USA to Argentina. Costa Rica: throughout.
Worker: color red; face smooth and shiny; mesosoma relatively compact, with dorsal face of propodeum shorter than posterior face; petiole with prominent anteroventral tooth.
This is one of the most remarkable of all army ant species. It has an extremely broad ecological tolerance. It occurs across a great latitudinal range, from the equator to the subtropics of both North and South America. It occurs in dry forest and wet forest, in primary forest and in second growth, in coffee farms and pastures, and in suburban yards. It occurs from sea level to high montane regions. The highest ant record I have for Costa Rica, a collection at 3000m near Villa Mills, is Labidus coecus.
The species is almost entirely subterranean, sometimes at considerable depth. On two occasions when residents living near La Selva Biological Station were having water wells dug at their residences they encountered L. coecus several meters down during excavations. When hand collecting, L. coecus is encountered under rocks and under leaf litter, and they are frequent in Winkler samples of sifted leaf litter. Perfecto (1992) observed a subterranean colony attacking a series of Dorymyrmex colonies in the open soil of a coffee farm. The Dorymyrmex had a dense population, with nests scattered over the farm, and the progress of the attacks could be followed by observing a sequence of nests from which the panicked Dorymyrmex workers were exploding to the surface.
Columns are occasionally seen on the surface. In Sirena station in Corcovado National Park, during my graduate student days, nocturnal L. coecus raids would occasionally swarm up through the cracks in the kitchen floor and forage on food scraps on the floor. I discovered this while carrying out my own nocturnal raids on the park's crackers and jelly, creeping in in the dark and hopping out with stinging feet. Twice I have seen columns emerging from the ground and attacking large scarab larvae writhing on the surface. Columns will also surface to cross hard-packed footpaths.
Labidus coecus is atypical of other New World army ants in its more generalized foraging habits. Although much of its diet is the brood of other ant species, they also scavenge dead food items, such as the scraps on the kitchen floor in Sirena. One morning in Monteverde I observed a massive raid emerging from the ground and attacking a plate of left over gallo pinto (rice and beans fried in oil) that had been left on a back step. It was curious and somewhat comical to see workers vigorously attacking oily rice grains with the same behaviors they use to attack other ants, biting and stinging individual grains and hauling them away (Fig. 1a,b).
In the study of army ants, most of the attention has focused on the large epigaeus species in the genus Eciton. But the highest density and most ecologically important army ants may turn out to be L. coecus. Kaspari and O'Donnell (2003) have estimated that every square meter of rainforest floor may be visited nearly daily by army ants, largely due to high densities of L. coecus found in sample plots of rainforest leaf litter.
Kaspari, M., and S. O'Donnell. 2003. High rates of army ant raids in the Neotropics and implications for ant colony and community structure. Evol. Ecol. Res. 5: 933-939.
Perfecto, I. 1992. Observations of a Labidus coecus (latreille) underground raid in the central highlands of Costa Rica. Psyche (Cambridge) 99:214-220.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. email@example.com
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