Odontomachus

Seen up close, a large Odontomachus worker moving slowly across the leaf litter in a dipterocarp forest in the Philippines (or elsewhere) is spectacular. The bizarre head of species of this genus bears strong jaw-muscles, and large, elongate trap-jaws which are carried sideways when foraging, ready to snap shut as potential prey comes in touch with the long frontal trigger hairs. A powerful stinger at the apex of the abdomen completes the image. These ants resemble nothing so much as small alligators lost among the dimensions of the litter. (Sorger and Zettel 2011)

Identification
Schmidt and Shattuck (2014) - Workers of Odontomachus are so distinctive that they are difficult to confuse with those of any other genus except Anochetus, the sister genus of Odontomachus. The unusual trap mandibles and head shape of Odontomachus are synapomorphic with Anochetus, but the genera are readily differentiated by examination of the posterior face of the head. In Odontomachus the nuchal carina is V-shaped medially, and the posterior surface of the head has a pair of dark converging apophyseal lines. In Anochetus the nuchal carina is continuously curved and the posterior surface of the head lacks visible apophyseal lines. These genera also tend to differ in size (Anochetus are generally smaller, though there is some overlap), propodeal teeth (absent in Odontomachus but usually present in Anochetus), and petiole shape (always coniform in Odontomachus, but variable in Anochetus).

Distribution
Schmidt and Shattuck (2014) - Odontomachus is abundant in the tropical and subtropical regions of the world, though it is most diverse in the Asian tropics and the Neotropics. Australia boasts a handful of species, while Africa has two species (Odontomachus assiniensis and Odontomachus troglodytes) and the Malagasy region has three species (Odontomachus coquereli, Odontomachus troglodytes, and Odontomachus simillimus, the latter apparently introduced to the Seychelles; Fisher & Smith, 2008). A few species extend into temperate regions, notably in the southwestern United States, northeastern China, central Argentina, and southwestern Australia (reviewed in Brown, 1976).

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



Biology
Hita Garcia, Wiesel and Fischer (2013) - Mainly tropical and subtropical in its distribution but some species can also be found in temperate zones or even in semi-desert areas (Brown, 1976). The more than 70 species are roughly equally split between the New and the Old World. Species of Odontomachus are large, often conspicuous ants that are mainly predaceous (Brown, 1976; Fisher & Smith, 2008). Like Anochetus, they are trap-jaw ants and can also use these specialised mandibles to jump away if they feel disturbed (Brown, 1976). They hunt other arthropods, often termites, but a few also tend hemipterans. They generally nest in the soil, the leaf litter, or in rotten logs while few species live arboreally (Brown, 1976)

Schmidt and Shattuck (2014) - In most respects Odontomachus are fairly typical ponerines. The nesting habits of many species have been observed, and most of these nest in soil or rotting wood (e.g., Odontomachus affinis: Brandão, 1983; Odontomachus bauri: Ehmer & Hölldobler, 1995; Odontomachus brunneus, Odontomachus clarus, Odontomachus relictus, and Odontomachus ruginodis: Deyrup & Cover, 2004; Odontomachus cephalotes: Wilson, 1959b; Odontomachus chelifer: Fowler, 1980; Passos & Oliveira, 2004; Odontomachus coquereli: Molet et al., 2007; Odontomachus erythrocephalus: Longino, 2013; Odontomachus opaciventris: de la Mora et al., 2007; Odontomachus rixosus: Ito et al., 1996; Odontomachus simillimus: Wilson, 1959b; van Walsum et al., 1998; Odontomachus tyrannicus: Wilson, 1959b), though some species will nest in more unusual locations such as in abandoned termite nests (Déjean et al., 1996, 1997) or arboreally (e.g., Odontomachus troglodytes: Colombel, 1972; O. brunneus, Odontomachus hastatus, and Odontomachus mayi; Brown, 1976; O. bauri and O. hastatus: Longino, 2013). The nests of O. bauri are apparently polydomous (Ehmer & Hölldobler, 1995). Odontomachus workers are monomorphic and are epigeic foragers, and some species are at least partially arboreal in their habits (Brown, 1976; Longino, 2013). Most species are generalist predators of arthopods, though many species partially specialize on certain types of prey, especially termites (e.g., Fowler, 1980; Lévieux, 1982; Ehmer & Hölldobler, 1995). At least some species will also tend honeydew-secreting insects or visit extrafloral nectaries (e.g., O. affinis: Borgmeier, 1920; O. bauri, O. hastatus, and Odontomachus panamensis: Schemske, 1982; Longino, 2013; O. troglodytes: Evans & Leston, 1971; Lachaud & Déjean, 1991a), and the Neotropical species O. chelifer is known to eat fruit and the arils of certain seeds, which the ants ultimately disperse (Pizo & Oliveira, 1998; Passos & Oliveira, 2002, 2004). Odontomachus laticeps and Odontomachus minutus (=Odontomachus meinerti) also collect seeds with nutritious arils (Horvitz & Beattie, 1980; Horvitz, 1981). ''350px|thumb|right|Copyright: Piotr Naskrecki

Colony size is highly variable across the genus, ranging from an average of only 18 workers in O. coquereli (Molet et al., 2007) to as many as 10,000 workers in O. opaciventris (de la Mora et al., 2007). Most species seem to have colony sizes of several hundred workers: O. chelifer colonies average between 100 to 650 workers (Fowler, 1980; Passos & Oliveira, 2004), colonies of O. rixosus had an average of 142 workers (Ito et al., 1996), and O. bauri is reported to have up to 300 workers per colony (Jaffe & Marcuse, 1983), though O. troglodytes colonies can have over 1,000 workers (Colombel, 1970a).

Most species of Odontomachus have typical winged queens and semi-claustral nest founding (Brown, 1976), though O. coquereli has wingless ergatoid queens and colonies apparently reproduce by division (Molet et al., 2007). An undescribed species from Malaysia is also reported to have ergatoid queens (Gobin et al., 2006), and colony reproduction by fission is suspected to occur in some other species (Brown, 1976). While some Odontomachus species are likely to be monogynous, many species are polygynous (e.g., Odontomachus assiniensis: Ledoux, 1952; O. cephalotes: Peeters, 1987; O. chelifer: Medeiros et al., 1992; O. rixosus: Ito et al., 1996; Odontomachus troglodytes: Ledoux, 1952). Queens of O. rixosus perform many of the tasks more typical of the worker caste, including foraging outside the nest (Ito et al., 1996). In the most detailed series of studies on a single Odontomachus species, Colombel examined various aspects of the behavior of O. troglodytes, including caste determination (Colombel, 1978), egg development (Colombel, 1974) reproduction by workers (Colombel, 1972), ecology, nest structure, demographics and population dynamics (Colombel, 1970a), egg-laying by queens (Colombel, 1970b), and alarm pheromones (Colombel, 1968). The laying of haploid eggs by workers has also been observed in O. chelifer (Medeiros et al., 1992), O. rixosus (Ito et al., 1996), and O. simillimus (van Walsum et al., 1998). Wheeler et al. (1999) examined the egg proteins of O. chelifer and O. clarus.

Only a handful of papers have been published on the social behavior of Odontomachus. Polyethism in Odontomachus troglodytes was studied by Déjean & Lachaud (1991), while division of labor in Odontomachus affinis was examined by Brandão (1983). Powell & Tschinkel (1999) discovered that the workers of Odontomachus brunneus organize themselves into a social hierarchy via ritualized dominance interactions, with repercussions for task specialization within the nest. Whether similar heirarchies exist among workers in other Odontomachus species is unknown, though dominance heirarchies exist among queens in colonies of the polygynous species Odontomachus chelifer (Medeiros et al., 1992). Jaffe & Marcuse (1983) observed both nestmate recognition and territorial aggression in Odontomachus bauri. Aspects of the mating behavior of Odontomachus assiniensis, the other African Odontomachus species, were studied by Ledoux (1952).

Wheeler & Blum (1973) identified the mandibular glands as the source of alarm pheromones in O. brunneus, O. clarus and O. hastatus. Morgan et al. (1999) examined the mandibular gland secretions of O. bauri, while Longhurst et al. (1978) studied the mandibular gland secretions of O. troglodytes and the response of males to these secretions. Oliveira & Hölldobler (1989) identified the roles of pygidial, mandibular and poison gland secretions in O. bauri for recruitment, alarm and attack behaviors. Alarmed Odontomachus workers can also stridulate (e.g. Carlin & Gladstein, 1989).

The trap mandibles and associated behaviors of Odontomachus (and Anochetus) rank among the most specialized of any ponerine. When hunting, Odontomachus workers hold their highly modified mandibles open at 180° and shut them with extreme force and speed on their prey. In fact, this is the fastest movement ever measured in any animal (Patek et al., 2006; Spagna et al., 2008). The contact of trigger setae (located beneath the mandibles) with the prey triggers the mandibular closure. The morphological, physiological and neurological characteristics of trap mandibles (and associated structures and behaviors) have been extensively studied (e.g., Gronenberg et al., 1993; Gronenberg & Tautz, 1994; Gronenberg, 1995a, 1995b; Ehmer & Gronenberg, 1997; Just & Gronenberg, 1999; Paul & Gronenberg, 1999; Spagna et al., 2008). Kinematic data indicate that the force of jaw closure in Odontomachus scales positively with body size, while acceleration scales inversely with body size (Spagna et al., 2008). The significance of these scaling relationships for the optimal foraging strategy in a given species is unknown.

The sequence of actions taken during prey capture by a hunting Odontomachus worker was summarized by de la Mora et al. (2007). Upon detection of a suitable prey item, the worker antennates it, then withdraws the antennae and snaps its mandibles shut on the prey. Generally the prey are held in the mandibles, lifted off the substrate, stung, and then transported back to the nest, though sometimes stinging is not necessary (Brown, 1976). The exact behavioral sequence used during prey capture varies somewhat depending on the Odontomachus species and the identity of the prey. For example, multiple mandibular strikes may be used to stun or dismember the prey. Odontomachus workers are often cautious during prey capture, especially with potentially dangerous prey such as termites. De la Mora et al. (2007) describe the predatory behavior of Odontomachus opaciventris in detail; the foraging behaviors of several other Odontomachus species have been described by other authors (e.g., Odontomachus assiniensis: Ledoux, 1952; Odontomachus bauri: Jaffe & Marcuse, 1983; O. chelifer: Fowler, 1980; Odontomachus troglodytes: Déjean, 1982, 1987; Déjean & Bashingwa, 1985). Déjean (1987) found that workers of O. troglodytes learn to avoid noxious prey.

Rapid mandibular strikes are used by Odontomachus to perform a variety of specialized tasks in addition to prey capture. Patek et al. (2006) found that workers of O. bauri utilize the force of their mandible strikes to bounce to safety (or to bounce onto intruders), and also to eject intruders away. This latter behavior (the bouncer defense) was studied in detail in O. ruginodis by Carlin & Gladstein (1989). In addition to these highly specialized tasks, the mandibles of Odontomachus remain functional for more typical activities such as nest construction and brood care (Just & Gronenberg, 1999).

Nomenclature

 *  ODONTOMACHUS [Ponerinae: Ponerini]
 * Odontomachus Latreille, 1804: 179. Type-species: Formica haematoda, by monotypy.
 * Odontomachus senior synonym of Pedetes: Dalla Torre, 1893: 51.
 * Odontomachus senior synonym of Champsomyrmex, Myrtoteras: Brown, 1976a: 67.
 * CHAMPSOMYRMEX [junior synonym of Odontomachus]
 * Champsomyrmex Emery, 1892d: 558 (footnote). Type-species: Odontomachus coquereli, by monotypy.
 * Champsomyrmex subgenus of Odontomachus: Forel, 1893a: 163; Forel, 1917: 238.
 * Champsomyrmex as genus: Emery, 1892d: 558 (footnote); Emery, 1911d: 111; Wheeler, W.M. 1922a: 653.
 * Champsomyrmex junior synonym of Odontomachus; Brown, 1976a: 96.
 * [ Thempsomyrmex Forel, 1893a: 163, incorrect subsequent spelling.]
 * MYRTOTERAS [junior synonym of Odontomachus]
 * Myrtoteras Matsumura, 1912: 191. Type-species: Myrtoteras kuroiwae, by monotypy.
 * Myrtoteras junior synonym of Odontomachus: Brown, 1976a: 96.
 * PEDETES [junior synonym of Odontomachus]
 * Pedetes Bernstein, 1861: 7. Type-species: Pedetes macrorhynchus, by monotypy.
 * Pedetes junior synonym of Odontomachus: Dalla Torre, 1893: 51.

Description
Schmidt and Shattuck (2014):

Worker
Medium to large (TL 6–20 mm; Brown, 1976) slender ants with the standard characters of Ponerini. Mandibles straight and narrow, articulating with the head medially, capable of being held open at 180°, and with a trio of large apical teeth and often a row of smaller teeth along the masticatory margin. Head with a pair of long trigger setae below the mandibles. Clypeus truncate laterally and anteriorly. Frontal lobes small and relatively widely spaced. Head strangely shaped: much longer than wide, with a distinct constriction behind the eyes and then often a gradual broadening posteriorly, the posterior margin of the head straight or mildly concave, the nuchal carina V-shaped medially, the posterior surface of the head with a pair of dark converging apophyseal lines. Eyes fairly large, located anterior of head midline on temporal prominences. Metanotal groove shallowly to deeply impressed. Propodeum broadly rounded dorsally, as broad as mesonotum but narrower than pronotum. Propodeal spiracles small, circular to ovoid. Metatibial spur formula (1s, 1p). Petiole surmounted by a conical node, topped by a posteriorly-directed spine of variable length. Gaster without a girdling constriction between pre- and postsclerites of A4. Stridulitrum almost always present on pretergite of A4. Head and body shiny to lightly striate, with very sparse pilosity and pubescence. Color variable, orange to black.

Queen
Similar to worker but slightly larger, alate and with the other caste differences typical for ponerines (Brown, 1976). Queens of O. coquereli are ergatoid (Molet et al., 2007).

Male
See descriptions in Brown (1976) and Yoshimura & Fisher (2007).

Larva
Larvae of various Odontomachus species have been described by Wheeler (1918), Wheeler & Wheeler (1952, 1964, 1971a, 1980), Brown (1976), and Petralia & Vinson (1980).