Attini, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
Colombia (type locality, see Kempf 1968), Costa Rica. Costa Rica: Atlantic slope, sea level to 800m elevation.
Mandibles with 5 teeth; preocular carina curving mesad toward frontal carina; antennal scrobe poorly defined; lateral vertex margins produced as acute teeth that project posterolaterally; pronotum lacking tubercles; anterior mesonotal tubercles very large.
Adams and Longino (2007) present a detailed natural history study of C. cornutus and its relationship with the social parasite Megalomyrmex mondabora.
Cyphomyrmex cornutus prefers mature forest understory or edge habitats that are still highly shaded. The nest is a large mass of accreted material, usually suspended from a vine stem, a tilted sapling trunk, or a narrow gauge branch, and typically 1-2m above the forest floor. Although usually exposed and suspended, I observed one nest in a cavity in the live trunk of a Xanthosoma (Araceae). The accreted material is dark brown, moist, and highly friable. It is not a carton or paper. Much of the nest volume is composed of this material, with chambers containing the ant colony in one portion of the mass. The nest is usually penetrated by epiphyte or vine roots, and there are often small epiphyte seedlings sprouting on the surface. However, the nests never form real ant gardens; there are never masses of large epiphytes on the nest. No other Cyphomyrmex species is known to make a large, exposed, arboreal nest.
Colonies can have large populations; Adams and Longino (2007) reported populations of 208, 1105, 2657, and 4117 workers in four dissected nests. Usually there is little surface activity, but twice I have seen columns of workers returning to the nest carrying particulate material.
Although they lack the ubiquity of the common species rimosus and salvini, they can be moderately abundant in lowland to mid-elevation primary rainforest. The nests are difficult to see at first. The first two meters above the ground in a mature forest, especially mid-elevation forest, is dark and cluttered with dead and live tree trunks, vines, roots, and suspended clots of rotting organic matter. But a dedicated attine biologist (like Rachelle Adams) can develop a search image for the nests, and they turn out to be more common than one might suppose.
The nests are home to more than the ants themselves. Various organisms inhabit the accreted soil. Twice I have found small colonies of the large ponerine ant Pachycondyla bugabensis in C. cornutus nests. Rachelle Adams also found a wide variety of ant species living in or on the nests she examined, and these are reported in Adams and Longino (2007). With the exception of M. mondabora, discussed below, all appear to be generalized arboreal ants, nesting opportunistically with C. cornutus.
Perhaps the most interesting inhabitants are colonies of Megalomyrmex mondabora. These shiny black ants have been found numerous times in the nests of C. cornutus. The entire colony can be found in chambers in close proximity to the chambers of the Cyphomyrmex. Rachelle Adams established subcolonies with C. cornutus and M. mondabora and observed behavioral interactions (Adams and Longino 2007). She discovered that the M. mondabora consume both larvae and fungus of their attine hosts and thus are clearly parasites. The attines respond submissively to their parasites.
Following are notes on individual nest collections:
During work at Pitilla station in Guanacaste Conservation Area, a mid-elevation wet forest site on the Atlantic slope of the Cordillera de Guanacaste, Scott Shaw pointed out to me a nest of Cyphomyrmex cornutus. It was a typical nest of accreted soil about half meter above ground. I noticed a number of Megalomyrmex mondabora workers moving on the surface, and entering through a hole. Dissection of the nest revealed a populous nest of Megalomyrmex, with brood and alate queens and males, in the center of the Cyphomyrmex next. The Megalomyrmex nest was completely surrounded by active portions of the Cyphomyrmex nest. On disturbance, there were occasional aggressive interactions between Cyphomyrmex and Megalomyrmex. There had been none (no aggressive interactions) prior to opening the nest.
During another visit to Pitilla, Dan Janzen brought in an entire nest from the forest. It was a typical exposed nest of accreted soil, with abundant beetle elytra inside and a few sprouting epiphytes on the surface. There were abundant males and alate queens. The nest material was filled with nematodes. A Pachycondyla bugabensis nest was embedded in the Cyphomyrmex nest. A single-queen Solenopsis nest was in a dead stick (Cecropia petiole?) that was also embedded in the Cyphomyrmex nest.
On 19 June 2002 I found a Cyphomyrmex cornutus nest in Braulio Carrillo National Park, at 500m elevation on the Volcan Barva transect. It was a suspended nest of accreted material. It contained not only the Cyphomyrmex colony, but also a colony of Megalomyrmex mondabora. The Cyphomyrmex seemed to have one entrance hole and the Megalomyrmex another. I saw an occasional Megalomyyrmex worker on the surface of the nest. The Megalomyrmex colony was large, with perhaps dozens to a hundred or more workers, abundant brood, and alate queens and males. The Cyphmyrmex were also abundant, with many beetle elytra incorporated in nest and gardens. They did not seem to act aggressively toward the Megalomyrmex workers. [Images of nest, with associated Megalomyrmex colony (click here).]
In January 1989 I made the following observations on a nest discovered at Casa Plastico, a mid-elevation site on the slopes above La Selva Biological Station. A nest of accreted soil was suspended from the lower surface of a horizontal treelet trunk, about 1m high. Epiphyte roots ramified through the upper half. Workers and fungus gardens were concentrated in upper half, near the roots. Workers, brood, and fungi were thinly spread, with no dense brood piles. The fungus was grown largely on dead beetle parts, including many elytra. The lower half of the nest tapered to a point and was composed of dense, solid material. This material was populated by large nematodes. Inquilines included nematodes, a few yellow silverfish, and a few small isopods. A tiny yellow Solenopsis was thinly scattered throughout. A Pachycondyla bugabensis worker was found with a few larvae in a small chamber toward the top. I sampled the bottom 4/5 of the nest of Cyphomyrmex and encountered only workers, brood, and two alate queens. I saw no colony queen, perhaps leaving her in the upper 1/5. [Images of nest: image-1, image-2, image-3.]
A nest was collected at La Selva that contained a single colony queen.
Image of a nest from Hitoy Cerere Reserve: image-1.
Adams, R. M. M., and J. T. Longino. 2007. Nesting biology of the arboreal fungus-growing ant Cyphomyrmex cornutus and behavioral interactions with the social-parasitic ant Megalomyrmex mondabora. Insectes Sociaux 54:136-143.
Kempf, W. W. 1968. A new species of Cyphomyrmex from Colombia, with further remarks on the genus (Hymenoptera, Formicidae). Rev. Brasil. Biol. 28:35-41.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.firstname.lastname@example.org
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