Anochetus

Found throughout the world's tropics and subtropics and represented by more than 100 species. The most recent revision is becoming somewhat dated (Brown 1978), along with its included key to species. Anochetus form small nests, usually with fewer than 100 workers, in soil, in termite nests, under logs and in rotten wood. A few species are arboreal. They are predacious on small invertebrates with some species known to specialise on termites, using their trap-like jaws and sting to capture and subdue prey. They commonly forage in leaf litter and are less frequently found in the open, especially when compared to workers of the closely related genus Odontomachus. Many species have been found to feign death when alarmed.

Identification
When viewed from the front, the outer surface of the head is complex, with narrow sections above and below bulging convexities which contain the eyes. The mandibles are long and straight, are inserted in the middle of the front margin of the head, and generally have only 2 or 3 large teeth near the tips (although they sometimes have small teeth along the inner margins which are much smaller than the teeth at the tips). The top of the head is uniformly coloured and lacks dark lines. The upper front of the head is usually smooth although it sometimes has a weak, ill-defined central groove.

The unique shape of the head and mandibles will separate these ants from all others except Odontomachus. Odontomachus and Anochetus can be easily distinguished by the characters on the back of the head. With head viewed from back near neck of pronotum, Odontomachus has dark, inverted V-shaped apophyseal lines that converge to form a distinct, sometimes shallow groove or ridge on upper back of head. In Anochetus, the V-shaped apophyseal lines are absent. In the same region of the back of head, however, nuchal carinae in Anochetus form an uninterrupted, inverted U-shaped ridge. Odontomachus and Anochetus 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).

In the field, small members of Anochetus might also be mistaken for Strumigenys, from which they may be distinguished by their one-segmented waist (vs. two segments in Strumigenys).

Distribution
Like its sister genus Odontomachus, Anochetus is widespread in the tropical and subtropical regions of the world. A few species encroach on temperate areas of South America, southern Africa, Europe (southern Spain), and Australia (reviewed in Brown, 1978).

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



Biology
Schmidt and Shattuck (2014) - Despite their interesting mandibular structures and associated behaviors, relatively little is known about the habits of Anochetus. Brown (1976, 1978) reviewed what was known about Anochetus at the time. Torres et al. (2000) performed the most detailed study of the ecology and behavior of a single Anochetus species (Anochetus kempfi), though the applicability of these observations to other species is uncertain. The lack of information on Anochetus likely stems from the fact that its sister genus, Odontomachus, is more conspicuous and more easily studied. Anochetus are generally smaller than Odontomachus (TL 3–12 mm versus TL 6–20 mm). Colonies of Anochetus also tend to be smaller, typically containing fewer than 100 workers versus several hundred for Odontomachus (Brown, 1976, 1978), though colonies of Anochetus faurei were found to have about 400 workers (Villet et al., 1991). Anochetus also tend to nest and forage more cryptically than the epigeic Odontomachus; when they do forage above ground, Anochetus are more likely to be nocturnal than are Odontomachus (Brown, 1978). Anochetus typically nest in tight places such as in rotten twigs, under bark, or in small spaces in the soil (Wilson, 1959b; Brown, 1976, 1978; Lattke, 1986), some are apparently arboreal (Brown, 1976, 1978), and some nest in termitaries (Wheeler, 1936; Déjean et al., 1996, 1997). Anochetus often feign death when disturbed, unlike Odontomachus, which tend to attack and sting intruders (Brown, 1978).

Like Odontomachus, Anochetus use their trap-jaws to catch insect prey and can also use their mandibles to bounce themselves away from danger (Brown, 1978). The structure and neurobiology of the Anochetus trap-jaw mechanism were studied by Gronenberg & Ehmer (1996). The hunting strategy used by Anochetus tends to be more like that of some dacetines than that of Odontomachus, in that they are slower (Gronenberg & Ehmer, 1996) and more liable to ambush prey than to actively seek them out (Brown, 1978; Schatz et al., 1999). Mandibular strikes on prey are followed by a paralyzing sting (Schatz et al., 1999). The prey preferences of most Anochetus are unknown, though many appear to be specialist predators of termites (e.g., A. traegordhi; Schatz et al., 1999).

Very little is known about the social and reproductive behavior of Anochetus. Ergatoid queens are apparently common, and some species (such as members of the Anochetus inermis group; Brown, 1978) have both ergatoid and alate queens, while others may have only ergatoids (e.g., Anochetus kempfi and an unidentified species from Indonesia; Torres et al., 2000; Gobin et al., 2006). Workers of Anochetus faurei, Anochetus bequaerti, and Anochetus katonae were found to lack ovarioles, which is fairly unusual among ponerines (Villet et al., 1991). Torres et al. (2000) observed a novel behavior in A. kempfi, in which nursery workers hold unhatched eggs in their mandibles until they hatch, and never allow them to be set down on the substrate of the nest. Another interesting behavior in this species involves the execution of excess queens by the workers of a colony.

The chemical ecology of Anochetus has received little attention, though Anochetus grandidieri (Madagascar) was reported to be a source of toxic alkaloids in poison frogs (Clark et al., 2005).

Castes
Most species have winged queens, but ergatoid queens have evolved sporadically in several species (e.g. A. kempfi, Torres et al. 2000). Workers in at least 4 species lack ovaries completely (Villet et al. 1991; F. Ito pers. comm.), and this may be characteristic of the whole genus, meaning that gamergate reproduction is impossible.

Nomenclature

 *  ANOCHETUS [Ponerinae: Ponerini]
 * Anochetus Mayr, 1861: 53. Type-species: Odontomachus ghilianii, by monotypy.
 * Anochetus senior synonym of Stenomyrmex: Forel, 1887: 382; Brown, 1978c: 552.
 * Anochetus senior synonym of Myrmapatetes: Brown, 1953h: 2.
 * MYRMAPATETES [junior synonym of Anochetus]
 * Myrmapatetes Wheeler, W.M. 1929b: 6. Type-species: Myrmapatetes filicornis, by original designation.
 * Myrmapatetes junior synonym of Anochetus: Brown, 1953h: 2.
 * STENOMYRMEX [junior synonym of Anochetus]
 * Stenomyrmex Mayr, 1862: 711. Type-species: Myrmecia emarginata, by subsequent designation of Wheeler, W.M. 1911f: 173.
 * Stenomyrmex subgenus of Anochetus: Dalla Torre, 1893: 47; Emery, 1911d: 110; Forel, 1917: 238; Kempf, 1964f: 237.
 * Stenomyrmex junior synonym of Anochetus: Brown, 1978c: 552.

Schmidt and Shattuck (2014):

Anochetus was erected by Mayr (1861) to house the species Odontomachus ghilianii Spinola. Like Odontomachus, Anochetus has had a stable taxonomic history at the genus level. Though Brown (1973) provisionally synonymized Anochetus under Odontomachus, he reversed himself (1976) after discovering the consistent differences in head structure between the two groups. Anochetus itself has two junior synonyms, Stenomyrmex (often treated as a subgenus of Anochetus; Mayr, 1862) and Myrmapatetes (Wheeler, 1929). Like Odontomachus, the history of family-level taxonomy for Anochetus has been complex (see discussion under Odontomachus). Schmidt's (2013) molecular phylogeny of Ponerinae confirms that Anochetus is a member of tribe Ponerini and that its sister group is Odontomachus. It is possible that Anochetus may not be mutually monophyletic with Odontomachus (see discussion under that genus), but we are retaining Anochetus as a distinct genus for now. This is consistent with the treatment by Santos et al. (2010), who could find no evidence that both are not monophyletic.

Worker
Small to medium (TL 3–12 mm; Brown, 1978) 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 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. Head strangely shaped: usually about as long as wide (sometimes longer than wide), with a gradual narrowing behind the eyes, the posterior margin of the head strongly concave, the nuchal carina continuously curved, and the posterior surface of the head without a pair of distinct apophyseal lines. Eyes small to moderate in size, located anterior of head midline on temporal prominences. Mesopleuron rarely divided by a transverse groove. Metanotal groove shallow to deep. Propodeum weakly to strongly narrowed dorsally, the posterior margins often with a pair of short spines or teeth. Propodeal spiracles small and round. Metatibial spur formula (1p) or (1s, 1p). Petiole variable, usually squamiform but sometimes coniform or nodiform, the posterodorsal apex often with one or two spines of variable length and acuity. Girdling constriction between pre- and postsclerites of A4 usually not apparent. Pretergite of A4 usually without a stridulitrum. Head and body shiny, striate or rugoreticulate, with sparse to abundant pilosity and little to no pubescence. Color variable, testaceous to dark brown.

Queen
Similar to worker but slightly larger, alate and with the other caste differences typical for ponerines (Brown, 1978). Ergatoid queens occur in many species; those of A. kempfi differ from conspecific workers by being smaller, with more differentiated thoracic sclerites and a larger gaster (Torres et al., 2000).

Male
See descriptions in Brown (1978) and Yoshimura & Fisher (2007).

Larva
Larvae of various Anochetus species have been described by Wheeler & Wheeler (1952, 1964, 1971a, 1976).