Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Range
Mexico to northern Argentina. Costa Rica: common in lowlands throughout.
Identification
Pronotum with a well-differentiated median eminence and a pair of dorsolateral (humeral) teeth; petiolar node as seen from the side low and thick, subtriangular, with broadly rounded summit, and anterior and posterior slopes strongly converging upward; color orange brown.
Natural History
Many naturalists have been drawn to the study of extrafloral nectaries by observing Ectatomma tuberculatum. Novices and specialists alike are drawn to these large ants and their curious behavior. Workers are common in young secondgrowth and forest edge habitats, foraging on plants bearing extrafloral nectaries. Passiflora and Inga are common nectaried plants, on whose newgrowth tuberculatum often may be found. Workers stand over individual nectaries, slowly gathering nectar as it is produced. They may gather a large glistening droplet, which they hold between their outstretched mandibles. They appear quite ferocious, because as you approach them they are alert to your presence, whirling to face you with gaping mandibles, and often not retreating. They are not as fierce as they look: the gaping mandibles are to maintain the nectar droplet, and when pressed they do not attack or sting, but rather run down the stem or drop from the plant. They are actually slow to sting, and you must hold them between your fingers for a few seconds to get stung.
Ectatomma tuberculatum occurs in both wet forest and dry forest habitats (Cook 1905, Weber 1946). Nests occur below ground, at the base of a tree or shrub stem, up the side of which workers construct a characteristic thatch chimney that serves as the entrance. The thatch chimney is approximately 2cm diameter (much wider than a worker) and may be up to 1m tall. The thatch is composed of fairly coarse fragments of vegetable matter, or less often mud. Cook (1905) excavated a number of colonies. He found that the nest was in the form of a tunnel one to three feet deep, with three to six small chambers. The queen with eggs and small larvae was usually in the lowest chamber, larger larvae in intermediate chambers, and pupae in the uppermost chambers. Some chambers contained insect remains and other debris, in which scavengers lived. Nest populations ranged from 100 to 400 or more workers, but was usually 200 to 300 workers. Some nests were polygynous, with 15 queens occurring in one. Males were present year round. Eggs laid by queens turned deep gray to blackish, while those laid by workers remained white. Workers covered larvae with dirt when they were ready to pupate. In observation colonies that Cook had transported to Texas, pupation took one and one-half hours. The pupal stage lasted 35.5 days for queens, 39 to 40.5 days for workers.
Colony foundation is partially claustral, in which queens form a hidden nest cell, and then forage for food. Dejean and Lachaud (1992) studied colony initiation in Quintana Roo, Mexico. Foundresses were usually found under dead wood or stones on the ground. In three cases foundresses were in myrmecophytic epiphytes (Schomburgkhia tibicinis, Tillandsia bulbosa). Dejean and Lachaud established ten foundresses in lab colonies, and observed them for 410 days. Queens foraged for carbohydrates, and both dead and live arthropods. When the first nanitics were produced, there was a period of mixed foraging when both queen and workers foraged. When the colony contained about a dozen workers the queen ceased foraging, and all foraging was done by the workers. Nanitic workers were relatively unaggressive and not very successful at capturing live prey. Post-nanitic workers were more aggressive, and increasingly foraged on live prey using an ambush technique. Dejean and Lachaud attributed the increased foraging efficiency of post-nanitic workers to a greater training period as nest guards at the nest entrance.
Workers are strictly arboreal foragers, issuing from the mouth of the tube and foraging up into the vegetation. They are much more common on low shrubby and viney vegetation than in the high canopy. They may be found foraging day and night. Workers are active predators of small arthropods, scavengers of dead arthropods, and avid collectors of extrafloral nectar. tuberculatum may have a propensity to prey on other social Hymenoptera near extrafloral nectaries. I have fequently seen workers carrying other ant species and stingless bees back toward the nest, and when I have placed dead stingless bees on leaves near tuberculatum workers, they have picked them up and returned to the nest.
Wheeler (1986) made a detailed study of the biology of tuberculatum on Barro Colorado Island, Panama. She observed that colonies have multiple nest entrances. The entrances are often damaged by digging predators or treefalls. She found 15 nest entrances in a mapped area of 243 square meters, which extrapolates to a density of 600 entrances per hectare. She made observations of foraging activity by recording numbers of out-bound and in-bound workers over 24hr time periods. On BCI she observed a mass exit at sunset, high foraging activity throughout the night, a decrease at sunrise, and a low level of foraging during the day. She made parallel observations at La Pacifica, a dry forest site in Costa Rica, and found a different pattern of foraging: high activity in the morning as well as at night, and no mass exit at dusk. Foraging workers returned with nectar droplets and prey. "Prey included ants (Odontomachus bauri (Emery) worker, Pheidole punctatissima Mayr soldier, Pheidole sp. minor worker, alate Azteca sp. queen, unidentified male ant, and Camponotus larva), other Hymenoptera (Polybia rejecta (F.), P. diguetana Buysson, and wasp or bee pupae), lepidopteran larvae up to 2.5cm long, termites (Nasutitermes ephratae (Holmgren) soldier and many termite workers), and other small insects such as a young mantid. Other prey items included a small (5mm) snail and frass containing insect parts." Social insects made up an important part of the prey spectrum.
McCluskey (1987) also observed increased nocturnal foraging in BCI tuberculatum, and studies with a colony fragment in controlled conditions suggested that the behavior might be circadian, and not determined by direct responses to temperature or light changes.
Wheeler (1986) observed an association between tuberculatum and Crematogaster limata. She found that C. limata often nested near the tuberculatum nest entrances, and at intervals large numbers of limata workers filed into the entrances in a raid-like fashion. The timing of the "raids" usually corresponded with times when a large number of tuberculatum workers were in the entrance tubes, such as the dawn and dusk peaks of worker movement. She observed limata workers climbing onto the backs of tuberculatum workers, which stood still as the smaller limata workers licked the dorsal surfaces of the head and back. No interspecific aggression was observed. She speculated that the relationship might be a facultative mutualism, in which the limata workers remove small amounts of nectar that leak onto the coarse surface sculpture of tuberculatum. She suggested the relationship might be similar to cleaner-fish associations seen in marine systems.
Ectatomma tuberculatum was considered a potential biological control agent in the early 1900's. O. F. Cook traveled to eastern Guatemala in 1902, and observed the ants tending extrafloral nectaries on cotton. Where the ants were abundant there were no weevils attacking the cotton. The association was apparently long known to indigenous people, who called the ant the "kelep" (Cook 1904). Cook attempted to introduce the species to cotton fields in Texas, but the attempt was unsuccessful (Weber 1946).
At La Selva Biological Station I observed a colony excavating a nest after a period of heavy rainfall. Workers were carrying particles of soil up out of the chimney-like mouth of the nest, over some arching vegetation to a point about 1m away from the nest, then dropping the particles. About a liter of soil had accumulated in a conical pile beneath the drop point. Thus, tuberculatum removes its excavated soil some distance from the nest. This behavior could be adaptive, by making the location of the nest entrance itself less conspicuous to predators.
Type data
Formica tuberculata Olivier 1792:498. Syntype worker, queen: Trinidad.
Literature Cited
Cook, O. F. 1904. An enemy of the cotton-boll-weevil. Science 19:862-864.
Cook, O. F. 1905. The social organization and breeding habits of the cotton-protecting kelep of Guatemala. U. S. Dep. Agric. Bur. Entomol. Tech. Ser. 10:1-55.
DeJean, A., and J. P. Lachaud. 1992. Growth-related changes in predation behavior in incipient colonies of the ponerine ant Ectatomma tuberculatum Olivier. Insectes Sociaux 39:129-143.
McCluskey, E. S. 1987. Circadian rhythm in the tropical ant Ectatomma (Hymenoptera Formicidae). Psyche (Camb.) 94:245-252.
Olivier, A. G. 1792. Encyclopedie Methodique. Histoire Naturelle. Insectes 6 (part 2):369-704. Paris. (Ants: pp. 469-506.)
Weber, N. A. 1946. Two common ponerine ants of possible economic significance, Ectatomma tuberculatum (Olivier) and E. ruidum Roger. Proc. Entomol. Soc. Wash. 48:1-16.
Wheeler, D. E. 1986. Ectatomma tuberculatum foraging biology and association with Crematogaster (Hymenoptera Formicidae). Ann. Entomol. Soc. Amer. 79:300-303.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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