Acromyrmex octospinosus (Reich, 1793)

Acromyrmex octospinosus is considered a significant agricultural pest.

Goncalves (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, Curaao 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.