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Extant: 3 valid subspecies
Acromyrmex octospinosus is a leaf cutting and fungus growing ant in the tribe Attini. The highly polymorphic workers are reddish brown to nearly black, and measure up to 7.5 mm in length. They are mainly characterized by the absence of median spines, the flattened shape of the lower pronotal spines which have a blunt or rounded tip, and sparse pubescence (Gonalves, 1961). Like its relatives in the closely related Atta, A. octospinosus workers harvest foliage from live plants. The foliage is brought back to specialized underground chambers and used to cultivate a fungus the ants depend upon for nutrition. Acromyrmex octospinosus is considered a significant agricultural pest (Cherrett & Peregrine, 1976). The species ranges from Mexico to northern South America and into the Caribbean.
Native range: Mexico to northern South America and into the Caribbean.
Introduced range: Caribbean: Carriacou, Curaao and Guadeloupe.
Goncalves (1961) provides a brief overview of the species, including its ecology. Acromyrmex octospinosus can live in a wide variety of habitats, including forests, open agricultural fields and backyards. Nests are shallow and tend to smaller than those of most Atta species, and can be formed in soil, under rocks, in ravines, atop tree buttress roots, in tree crevasses, and opportunistically beneath artificial substrates including sheet metal, cement and roofing slates (Urich, 1895; Weber, 1945; Wetterer et al., 1998). The species also harvests a wide variety of vegetable matter (Wetterer et al., 1998)
Acromyrmex octospinosus is currently in the process of expanding its range into the Caribbean. Populations have recently been introduced to Carriacou, Curaao and Guadeloupe and appear to be spreading (Cherrett, 1968; Cherrett & Peregrine, 1976; Mikheyev, 2008; Pollard, 1982; Solomon, 2007). The Guadeloupe population is believed to have most likely originated from a single-queen introduction from Trinidad and Tobago, although northeastern South America is also a possibility (Mikheyev, 2008; Mikheyev et al., 2006). Spread of the Guadeloupe population is slow and even (0.51 0.20 km/year). The inadvertent transport of the species may be limited by the large size and easy detection of A. octospinosus queens (Mikheyev, 2008). Another factor working to limit future introductions is that the species requires large excavated cavities for their fungus gardens (Mikheyev, 2008; Wetterer et al., 1998).In Costa Rica (Jack Longino)
At La Selva Biological Station Acromyrmex octospinosus nests near ground level in mature forest. Nests have been observed in the bases of dead trees and under a piece of broken cement culvert in the leaf litter.
On 17 March 1993, mid dry season, I observed many alates, mainly queens, at La Selva Biological Station. They were at the lab clearing blacklight at 6:00am, suggesting a predawn nuptial flight.
Wetterer (1991) reports quantitative data on the foraging ecology of the species at La Selva.
Fernandez-Marin et al. (2003) report on nest founding behavior:
(Abstract) Foundresses of the leaf-cutting ant Acromyrmex octospinosus in central Panama forage for leaves as garden substrate (semi-claustral foundation). The fungal pellet and substrate usually are attached to rootlets, which are used as a platform for the garden. This arrangement keeps the garden suspended away from the earthen chamber of the underground nest during early colony growth, and we hypothesize that it serves to minimize contact between the garden and contaminants. A. octospinosus foundresses produce from 3 to 7 workers in 2.7 months after founding the nest, but workers do not forage for substrate at this time. Incipient nests died or were abandoned at a monthly rate of ca. 50%. We show that ants routinely clean their legs before manipulating the garden substrate. We also describe how foundresses use their fore-legs to rub the surface of the metapleural gland, and they then use typical grooming behaviors to pass the forelegs through the mouthparts, after which the ant then licks the garden substrate. Similarly, ants apparently use their mouths to transfer fecal droplets to their legs. We briefly discuss the functional significance of these grooming behaviors, and hypothesize that they are prophylactic behaviors that may help the foundress maintain a hygienic garden.
Diagnosis among workers of introduced and commonly intercepted species. Antennae 11-segmented. Antennal club indistinct. Antennal scrobe lacking. Eyes medium to large (greater than 5 facets), but distinctly less than half head length. Antennal insertion not surrounded by a raised sharp-edged ridge. Frontal lobes do not obscure face outline between mandible and eye. Posterolateral corners of head spinose. Mandibles triangular. Dorsum of promesonotum with 3 pairs of spines or teeth. Propodeum armed with spines or teeth. Waist 2-segmented. Petiole with a distinct and upright node. Postpetiole attached to lower surface of gaster. First gastral tergite with numerous tubercles. Color reddish brown to nearly black.
Acromyrmex octospinosus is distinguished from closely related Atta species by the presence of three spines on the promesonotum (two in Atta), and the presence of tubercles on the first gastral tergite. The species is distinguished from its only congener native to the United States (A. versicolor Pergande) by its distinctly longer promesonotal spines and distinctly less sculptured head and body.
Cherrett, J.M. (1968) Some aspects of the distribution of pest species of leafcutting ants in the Caribbean. Proc. Am. Soc. Hortic. Sci. Trop. Reg., 12, 295-310.
Cherrett, J.M. & Peregrine, D.J. (1976) A review of the status of leaf-cutting ants and their control. Ann. Appl. Biol., 84, 124-128.
Gonalves, C.R. (1961) O genero Acromyrmex no Brasil (Hym. Formicidae). Stud. Entomol., 4, 113-180.
Fernandez-Marin, H., J. K. Zimmermann, and W. T. Wcislo. 2003. Nest-founding in Acromyrmex octospinosus (Hymenoptera, Formicidae, Attini): demography and putative prophylactic behaviors. Insectes Sociaux 50:304-308. Hlldobler, B. & Wilson, E.O. (1990) The ants. Harvard University Press, Cambridge, Mass., xii + 732 pp.
Kliejunas, J.T., Tkacz, B.M., Burdsall, H.H., Jr., DeNitto, G.A., Eglitis, A., Haugen, D.A. & Wallner, W.E. (2001) Pest risk assessment of the importation into the United States of unprocessed Eucalyptus logs and chips from South America. U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. Madison, WI, General Technical Report FPL-GTR-124, 134 p.
Mikheyev, A.S. (2008) History, genetics and pathology of a leaf-cutting ant introduction: a case study of the Guadeloupe invasion. Biol. Invasions, 10, 467-473.
Mikheyev, A.S., Mueller, U.G. & Abbot, P. (2006) Cryptic sex and many-to-one coevolution in the fungus-growing ant symbiosis. Proc. Natl. Acad. Sci. U.S.A., 103, 10702-10706.
Pollard, G.V. (1982) A review of the distribution, economic importance and control of leaf-cutting ants in the Caribbean Region, with an analysis of current control programmes. In: Brathwaite, C.W.D. & Pollard, G.V. (Eds.) Urgent plant pest and disease problems in the Caribbean. IICA, Port of Spain, pp. 43-61.
Schultz, T. R., D. Bekkevold, and J. J. Boomsma. 1998. Acromyrmex insinuator new species: an incipient social parasite of fungus-growing ants. Insectes Sociaux 45:457-471. Solomon, S.E. (2007) Biogeography and evolution of widespread leafcutting ants, Atta spp. (Formicidae, Attini). Ph.D. thesis, The University of Texas at Austin, xi + 95 p.
Urich, F.W. (1895) Notes on some fungus-growing ants in Trinidad. J. Trinidad Field Nat. Club, 2, 175-182.
Weber, N.A. (1945) The biology of the fungus-growing ants. Part VIII. The Trinidad, B. W. I., species. Rev. Entomol. (Rio de Janeiro), 16, 1-88.
Wetterer, J. K. 1991. Foraging ecology of the leaf-cutting ant Acromyrmex octospinosus in a Costa Rican rain forest. Psyche 98:361-371.
Wetterer, J.K., Gruner, D.S. & Lopez, J.E. (1998) Foraging and nesting ecology of Acromyrmex octospinosus (Hymenoptera: Formicidae) in a Costa Rican tropical dry forest. Florida Entomol., 81, 61-67.
Found most commonly in these habitats: 1 times found in SSA, 5 times found in lowland wet forest, 5 times found in lowland rainforest, 4 times found in montane wet forest, 1 times found in edge pasture/trop. wet forest, 2 times found in tropical wet forest, 2 times found in urban, 1 times found in deciduous forest, 1 times found in near comedor, 1 times found in STR, ...
Found most commonly in these microhabitats: 7 times at bait, acromyrmex; abundant alates, primarily queens, at blacklight at 0600hrs times 3396-s, 1 times Hojarasca, 3 times ex sifted leaf litter, 2 times nocturnal strays, 2 times ground, 1 times fungus garden under stone, 1 times Foraging leaves, 1 times column, 2 times beating vegetation, 2 times beating veg., ...
Collected most commonly using these methods: 3 times Blacklight, 3 times Winkler, 8 times search, 7 times Baiting, 5 times hand collecting, 4 times Malaise, 4 times beating, 2 times direct collection, 2 times flight intercept trap, 1 times Hand, 2 times Sweeping, ...
Elevations: collected from 5 - 1090 meters, 234 meters average
Type specimens: syntype of Acromyrmex octospinosus: casent0900490