Cyphomyrmex rimosus
Cyphomyrmex rimosus is a small dull brown to blackish brown ant with deep antennal scrobes, enlarged frontal lobes that obscure the lateral margins of the face, no propodeal spines, an apedunculate petiole, tubercles on the mesosoma, and appressed scale-like hairs. These ants are sometimes difficult to detect on account of their small size, slow movement and tendency to become immobile and even feign death when disturbed. Cyphomyrmex rimosus has a monomorphic worker caste and is considered one of the ‘lower’ attines and cultivates fungus gardens grown on scavenged vegetable matter, dead insects and insect fras. The species is native to the Neotropics, but has established introduced populations in the southern United States and the Galapagos islands. It is not considered a significant pest species in its native or introduced range.
The species is part of a complex of closely related and highly variable taxa that can be difficult to distinguish (Kempf, 1966 (1965)). Snelling and Longino (1992)revised the C. rimosus group and split it into five subgroups. The rimosus subgroup contains seven species, including C. rimosus and its close relative C. minutus. Both species occur in Florida, but whereas C. rimosus is argued to be introduced on the grounds that it has spread rapidly since it was first detected, Cyphomyrmex minutus is considered native (Deyrup, 1991). Cyphomyrmex minutus was treated as a junior synonym of C. rimosus prior to the revision of Snelling and Longino (1992), so it is difficult to determine which species earlier studies are referring to. For example, many of the Neotropical and North American records in the literature refer to the more widespread C. minutus (Snelling & Longino, 1992).
Cyphomyrmex rimosus usually live in colonies of less than 100 workers, but colonies of over 300 workers have been observed (Murakami & Higashi, 1997). Most colonies are usually monogynous, but there are reports of some polygynous colonies as well (Murakami & Higashi, 1997; Snelling & Longino, 1992). The fungus gardens are composed of yeasts in the unicellular phase rather than in the multicellular, mycelial phase typical of all other attine gardens (Mehdiabadi & Schultz, 2010). In addition to feeding on the yeast fungus grown in their gardens, C. rimosus is also known to take the nectar and sap of plants (Murakami & Higashi, 1997). The queens are reported to practice monandry and semi-claustral nest founding (Mehdiabadi & Schultz, 2010; Tschinkel, 1987). Nests are frequently simple, shallow, impermanent structures under rocks, logs or any other surface, and the species prefers open habitats. Further details of the natural history of C. rimosus, in is given in Mehdiabadi & Schultz (2010), Murakami & Higashi (1997)and Snelling and Longino (1992).
Not considered a significant pest species.
Diagnosis of worker among Antkey species. Antenna 11-segmented. Antennal club 2-segmented. Antennal scapes easily extended beyond eye level. Antennal scrobe present and well developed. Eyes medium to large (greater than 6 facets) but distinctly less than half head length. Eyes located below antennal scrobe near midline of head. Frontal lobes obscure face outline between mandible and eye. Posterolateral corners of head unarmed, without spines. Mandibles triangular. Pronotal spines absent. Propodeum lacking spines or teeth, but tubercles are present. Waist 2-segmented. Spongiform not attached to any portion of waist. Dull brown to blackish brown. Surfaces with appressed scale-like hairs.
Among Antkey species, C. rimosus is most likely confused with C. minutus. Snelling and Longino (1992) separate the two species by the following characters. The head width of C. rimosus is greater (0.62 mm versus 0.56 mm), and in C. rimosus the hairs on first gastral tergite are not completely appressed and separated by less than their own lengths whereas those of C. minutus are closely appressed and usually separated by more than their own lengths.
Among other introduced and commonly intercepted ants in the United States, C. rimosus can be distinguished the enlarged frontal lobes that obscure the lateral margins of the face, 11-segmented antenna, deep antennal scrobes, indistinct antennal club, and lack of propodeal spines. The antennal scrobes and lack of spines separates C. rimosus from other attine genera (Acromyrmex and Atta). Cephalotes species also have enlarged frontal lobes that obscure the lateral face margins, but C. rimosus can be distinguished from them by the eyes which are placed below antennal scrobe near midline of head (as opposed to at or near apex of antennal scrobe in Cephalotes).
Native Range (Snelling & Longino, 1992). Neotropics. Argentina, Brazil, Guinanas, Venezuala.
Introduced Range. Galapagos: Isabella, Santa Cruz. United States (Snelling & Longino, 1992): Alabama, Florida, Georgia, Mississippi.