Labidus

With seven described species, Labidus is a relatively small but widely distributed genus. Its members are more generalized predators than most other New World army ants and may have the greatest overall ecological impact due to high densities.

Identification
Diagnosis. Worker. Labidus workers are easily recognized by a combination of spiracle positioned high on the propodeum, 12-segmented antennae, propodeum not armed with spines or cuticular lamellae, short propodeal lobes, two-segmented waist, metatibial gland present, and pretarsal claws with a tooth. Labidus belongs to New World army ants with an unarmed propodeum and it could only be confused with Cheliomyrmex and certain larger species of Neivamyrmex. The former have one-segmented waist, and the latter always lack teeth on pretarsal claws.

Species richness
Species richness by country based on regional taxon lists (countries with darker colours are more species-rich). View Data



Biology
Labidus are often the most common army ants throughout their range, with up to three species occurring in a given area (do Nascimiento et al. 2004, author’s personal observations). They nest mostly underground (Fowler 1979) and forage in swarm raids. It is unclear whether brood production is synchronized; colonies appear to emigrate infrequently, their bivouacs staying in place for prolonged periods of time (Fowler 1979). Rettenmeyer (1963) and Fowler (1979) detailed the biology of Labidus praedator. The bivouacs are found in rotten logs or are subterranean, occupying preformed cavities such as abandoned nest chambers of Atta leaf-cutting ants (Rettenmeyer 1963, Monteiro et al. 2008). Mature colonies have been estimated to contain up to a million individuals (Fowler 1979). Labidus forages in swarm raids similar to those of Eciton burchellii (Rettenmeyer 1963) and its species are even more generalized predators that in addition to ant brood will take a variety of other arthropods, sugar, and plant parts, including flowers, seeds, fruit, and even processed food such as boiled rice (Borgmeier 1955, Monteiro et al. 2008). The two best-studies species, L. coecus and L. praedator, are similar in this respect and data on other species is lacking. Henry Walter Bates (1863) described L. coecus constructing soil tunnels over its raiding columns. Monteiro et al. (2008) studied L. praedator in agricultural lands in Brazil, finding that Lepidoptera caterpillars were the most common type of prey, followed by arils of many plant species and various non-Lepidopteran arthropods, both in adult and larval stages. Fowler (1979) observed the same species in Paraguay and reported that it frequently raided other ant colonies. The raids occur mostly during the day, although nocturnal activity is also substantial (O’Donnell et al. 2009). Perfecto (1992) observed an underground raid of L. coecus on several ant species. The reproductive biology of Labidus is poorly known. There is conflicting evidence as to whether brood production is synchronized or not, with available brood samples consisting of immatures at one or multiple stages of development and queen specimens with either extended or contracted gasters (Rettenmeyer 1963). Given the rarity of emigrations and confirmed existence of long-term bivouac sites, lasting up to eight months (Fowler 1979), it is possible that Labidus queens retain the ability to lay eggs in pulses but do not cease brood production long enough for non-overlapping brood cohorts to emerge and for colonies to exhibit the nomadic-statary cycle characteristic of Eciton.

Nomenclature

 *  LABIDUS [Ecitoninae: Ecitonini]
 * Labidus Jurine, 1807: 282. Type-species: Labidus latreillii (junior synonym of Formica coeca), by monotypy.
 * Labidus subgenus of Mutilla: Blanchard, in Cuvier, 1846: pl. 118, fig. 2.
 * Labidus junior synonym of Eciton: Dalla Torre, 1893: 1.
 * Labidus revived from synonymy as subgenus of Eciton: Emery, 1910b: 21.
 * Labidus revived status as genus: Borgmeier, 1953: 4.
 * Labidus senior synonym of Nycteresia, Pseudodichthadia: Emery, 1910b: 21; Borgmeier, 1955: 80.
 * NYCTERESIA [junior synonym of Labidus]
 * Nycteresia Roger, 1861a: 21. Type-species: Formica coeca, by monotypy.
 * Nycteresia junior synonym of Eciton: Mayr, 1865: 76.
 * Nycteresia junior synonym of Labidus: Emery, 1910b: 21; Borgmeier, 1955: 80.
 * PSEUDODICHTHADIA [junior synonym of Labidus]
 * Pseudodichthadia André, 1885: 838. Type-species: Pseudodichthadia incerta (junior synonym of Formica coeca), by monotypy.
 * Pseudodichthadia junior synonym of Eciton: André, in Forel, 1899c: 160 (footnote).
 * Pseudodichthadia junior synonym of Labidus: Emery, 1910b: 21.

Male
Shuckard (1840) - Char. Body elongate, cylindrical.

Head small, short, transverse, flat.

Antennae varying in length, usually setaceous, curved and inserted within two facial projections (forming vertical carinae) upon the anterior margin of the nearly obsolete clypeus, the scape never more than one-fourth the length of the flagellum, the apex of which frequently extends as far back as the insertion of the superior wings.

Eyes large, lateral, subglobose, and very prominent.

Ocelli large and very prominent, and placed in a curve upon the vertex.

Mandibles elongate, slender, arcuate, and forcipate, always leaving an open space usually semicircular between them and the clypeus.

Labrum triangular, the apex rounded, and in repose shutting down upon and inclosing the internal trophi.

Maxillary palpi two-jointed, shorter than the labial?

Labial palpi two-jointed, slender, the basal joint the longest.

Labium triangular.

Thorax ovate, gibbous: prothorax extending laterally to the insertion of the wings, which is at about half the length of the thorax: scutellum transverse: metathorax perpendicular and abruptly truncated.

Superior wings usually as long or longer than the abdomen, rarely shorter, with one marginal and three submarginal cells, which vary in form in the species, and one recurrent nervure, which is inserted about the middle of the second submarginal cell.

Legs varying in length in the species: coxae large, not deeply excavated above: trochanters small, triangular: femora and tibiae cylindrical, all the latter with a single calcar at their apex, which is usually dilated at the base: tarsi long and slender, the basal joint the most robust and the longest, the remainder decreasing in length, excepting the terminal one, which is a little longer than the penultimate: claws armed with a minute tooth just within the apex, and furnished with a small pulvillus within their fork.

Abdomen cylindrical, slightly curved, the segments frequently slightly constricted, the basal one forming a variously constructed peduncle, occasionally either flat or concave above, but most frequently transversely convex, and ... always separated from the following by a deep incisure. Penultimate and antepenultimate segments subequal, and the terminal one strictly compressed vertically at its apex, where it is profoundly emarginate. The male sexual organ usually protruding in the form of a deeply canaliculated and ernarginated plate or two acuminated compressed and curved spines.