ID guide | introduced ants

Acromyrmex octospinosus

General description: 

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 (Gonçalves, 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.


Gonçalves (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., 1998b). The species also harvests a wide variety of vegetable matter (Wetterer et al., 1998b).

Acromyrmex octospinosus is currently in the process of expanding its range into the Caribbean. Populations have recently been introduced to Carriacou, Curaçao 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., 1998b).

Risk statement: 

Acromyrmex octospinosus is considered a significant agricultural pest.

Diagnostic description: 

Diagnosis of worker among Antkey species. Antennae 11-segmented. Antennal club indistinct. Antennal scrobe lacking. Eyes medium to large (greater than 6 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.

Look alikes: 

Atta cephalotes, Atta sexdens.


Native range. Mexico to northern South America and into the Caribbean.
Introduced range. Includes Carriacou, Curaçao and Guadeloupe.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith