Bullet Ant (Paraponera clavata)
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Paraponera clavata is a common and conspicuous inhabitant of lowland moist and wet habitats in much of the neotropics. It is commonly known as the bullet ant because of its very painful sting, or the giant tropical ant because of its large size, up to 2.5 cm in length. It is also noteworthy on account of its taxonomic position. Its behavior and ecological relations have been relatively well studied, providing a window into the adaptive tools available to ants as they evolve.
P. clavata is the single known member of the subfamily Paraponerinae . For many years, based on superficial similarities, it was placed in the Ectatomminae, where it was thought to be most closely related to the genera Ectatomma and Rhytidoponera. Molecular studies have since revealed a substantial distance between Paraponera and the ectatommines, with Paraponera closer to the subfamily Ponerinae and the Ectatomminae closer to the Myrmicinae. This distinction is important, because many of the earlier publications on Paraponera characterize it as primitive and look to build insights into the evolution of social mechanisms in ants by considering Paraponera and Ectatomma365体育网站 as part of a closely knit evolutionary sequence. Present-day understanding is that these arguments were based on false phylogenetic assumptions.
Distribution and Nests
Paraponera365体育网站 is found only in the neotropics from Bolivia in the south to northern Central America and spanning nearly the entire breadth of South America east of the Andes. Within this range, it is most common at low to mid-elevations (1000 m and below) in habitats with more than 1.5 m of rain distributed relatively evenly through the year. While common in undisturbed forest habitats, it is also found in secondary forest.
Paraponera nests are typically found in the soil at the base of large trees, but much of the foraging activity is in the forest canopy. Each colony is founded by a single queen and can grow to contain up to 2000–3000 workers. In two forests in which nest distribution was mapped – Barro Colorado Island in Panama and La Selva Biological Station in Costa Rica – nests were regularly spaced at roughly 20-m intervals. This even distribution suggests territoriality, and in fact lethal combat among workers from different colonies is often observed .
Foraging workers vary somewhat in size, but all foragers are at the larger end of this species’s size range . The largest workers participate in defending the colony against major disturbances. Smaller workers, rarely seen outside the nest, apparently participate in brood care. This pattern of large, unimodal size variation amongworkers, coupled with size-specific task specialization, is common but certainly not universal in ants. Workers display some allometry, with larger workers having disproportionately large heads.
Orientation and Navigation
Paraponera workers have strong visual orientation capabilities in addition to their ability to follow pheromone trails [1, 8365体育网站]. They use landmarks in navigation and also visually orient to prey. Much of their foraging activity is at night, particularly during dry seasons, and they have noteworthy skills in visual navigation under conditions with minimal light.
Given the large biomass of each worker and of the colony as a whole, it is not surprising that Paraponera requires effective defense against predators. Their highly potent venom makes this possibly the world’s most painful stinging insect. The stinger is long (3–4 mm), so that a worker can deliver venom deep into the tissue of a potential predator . Some Amazonian indigenous peoples employ Paraponera stings in male initiation rituals . Additionally, workers are protected chemically by a noxious and highly odorous compound. Few vertebrates attempt to prey on this ant, and insect predators, such as army ants, tend to ignore or avoid Paraponera nests. A phorid fly, Apocephalus paraponerae, orients to the chemical defense of the workers and then parasitizes adults by laying its eggs on them .
The bullet ant, Paraponera clavata365体育网站, is among the emblematic species of neotropical rainforests. Remarkable for its size and the intensity of its sting, it is an unusually good study organism, as colonies are easily located and the workers are large enough to make observations of individuals feasible. This species has many of the physiological and behavioral adaptations associated with the ecological success of ants, including recruitment of nestmates to food, size-based behavioral castes, and highly effective colony defenses.
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