Cerapachys

These ants are not commonly encountered due to their cryptic, subterranean habitats. Nests and/or nest fragments are occasionally found under stones, in the soil or under, and in, logs and branches. Garcia, Wiesel and Fischer (2013) summarized the genus as follows: Cerapachys ants are specialised predators of other ants that conduct raids to attack prey nests. They retrieve captured larvae and pupae, less commonly also adults, to their own colony and store them as food (Hölldobler, 1982; Brown, 1975). Wilson (1958) and later Brown (1975) raised the question of whether Cerapachys and other members of the subfamily are nomadic, and proposing that nomadism might have evolved as special adaptation in ant-hunting cerapachyines in order to avoid depletion of prey. Members of this genus can be encountered in a variety of habitats ranging from humid rainforests to arid savannah grasslands or semi-deserts, and nests are generally constructed in the ground or in rotten wood (Brown, 1975). Cerapachys is widely distributed across the World's tropics and subtropics but most species occur in the Old World (Brown, 1975; Bolton, 2012). Although treated by Brown (1975) on a global base, the taxonomy of this genus is far from satisfactory, especially for the Afrotropical region. Brown (1975) listed around 20 described species from this region and presented an identification key to the worker caste, but postponed a formal revision until more material would become available. He also presented some doubts on the species status of some species, and mentioned the existence of several undescribed species. Identification to species level with Brown's (1975) key is often unreliable.

Identification
Species of Cerapachys are most often confused with ponerines (ants of the subfamily Ponerinae) but differ in having the frontal lobes very narrow so that the antennal sockets are completely visible when viewed from the front.

Within Australia, Cerapachys can be separated from Sphinctomyrmex (the only other Australian genus in what used to be the subfamily Cerapachyinae) by the shape of the gaster. In Cerapachys, the joints between the last 4 segments of the gaster are smooth so that in profile the their upper surfaces form a smooth outline. In Sphinctomyrmex, these segments are separated from each other by distinct constrictions so that in profile the outline is a series of convexities.

Most species of Australian Cerapachys have elongate, cylindrical bodies that are red or black (or less commonly yellow) and shiny. For protection during raids, species of Cerapachys have developed a relatively heavy integument with numerous sharp angles and teeth. Some species also have a ridge along the side of the petiole and often the mesosoma as well. The compound eyes can be large, small, or absent.

Brown (1975) - Worker Postpetiolar segment (true abdominal segment III) strongly constricted from body of gaster and varying greatly from species to species in size relative to petiole and to true abdominal segment IV, which always is the largest gastric segment. In the more extreme forms of the fragosus and edentatus groups, the petiole and postpetiole form 2 nodes that are small in comparison to segment IV, which covers and forms most of the gaster as in most Myrmicinae. No strong constriction between principal gastric segments. Antennae 9-12 segmented, often with a swollen apical segment. Palpi segmented 4,3 to 2,2. Compound eyes varying from large and multifaceted to completely absent. Ocelli present in workers in a minority of species. Tibial spurs on middle legs; tarsal claws simple or with a submedian tooth. Queen Usually winged, but sometimes wingless and ergatoid, always with compound eyes present so far as known, though they may be very small. Characters otherwise as in the worker of the same species, but body usually a little broader, segment for segment. Wings, when present, like those of male. Male See characterization under tribe Cerapachyini (p. 15). So far as known, the male of Cerapachys always has 13-merous antennae and apical spurs on the midtibiae, and the mandibles are triangular, though often with acute apex and concave masticatory border.

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



Biology
Species of Cerapachys are specialist predators of other ants and show "army ant" behavior during foraging. Workers are often encountered as individual scouts, small groups or huge columns. They hunt during the day in long files over the ground surface (or occasionally into trees) with many workers moving rapidly together in a loose column. In some cases, they will use scouts to find a suitable nest to raid, these initial scouts then returning to their home nest to recruit additional workers for a full-fledged raid. Chemical trails are laid during raids which are used by workers returning to the nest with prey, either singly or in small groups.

During raids, larvae in the attacked nest are stung and paralysed but not killed. They are then taken back to the host nest where they can survive in this paralysed state for an extended period without increasing in size or pupating. Workers, queens and larvae of Cerapachys all feed on the prey larvae, and this food source can be used during extended periods of non-foraging.

Nests occur in a wide range of sites, most commonly directly in the soil with single, small, simple entrance holes; under rocks; in cracks or between slabs of rock; in rotten wood on or in the ground; less commonly they nest in hollow twigs and beetle borrows in vegetation. Colonies are fairly small, normally with several tens to several hundred workers. Most species will disperse quickly when disturbed but some of the smaller species will lay motionless. Males are attrached to lights at night. A California species has been found walking within a column of a species of Neivamyrmex. In some species workers vibrate their antennae rapidly when foraging.

Fossil species are known from the Oligocene (35-25 million years before present).

Brown (1975) - The prey of several species of Cerapachys living in forested areas of the Old World is usually recorded as small or medium-sized species of Pheidole, but Wilson has also recorded Strumigenys and Lordomyrma species serving as prey in Melanesian forests, while species of Iridomyrmex and Melophorus are raided in more arid, open parts of Australia.

Most species of Cerapachys and Sphinctomyrmex appear to nest in the ground or in rotten wood. Nests I have seen in moist forested areas usually have one or a few relatively capacious chambers connected to the surface by a short passage, but in arid areas, there may be several chambers 10-50 cm or more deep in the soil, with longer tunnels. Sometimes the nest is under a rock. The entrance is usually an inconspicuous hole without a crater, but in a few cases, a small crater or turret occurs at the surface.

Nest populations can contain as few as 20 adult workers to more than a thousand; the higher counts hold for some species of Sphinctomyrmex and the Cerapachys typhlus and antennatus groups, but most Cerapachys nests probably contain less than 200 workers. Pupae are normally enclosed in cocoons. The winged males are very active when mature and may attempt to take flight when the nest is opened.

The means of nest-founding of cerapachyines is unknown. In southwestern Australia, Clark (1923, 1924) found solitary individuals of Cerapachys angustatus and Cerapachys constrictus under a stone and a log respectively, and thought that the latter, at least, was founding a nest. However, it is not even certain that these specimens were reproductives, let alone founding queens, since no brood was found with either one, and both are “ergatoid” (i.e., possibly worker) in form.

Worker Morphology
Borowiec (2009) used the following terms in his revision of the Cerapachys sexspinus species group;

The term ‘parafrontal ridges’ is derived from Wilson’s (1964) work on Aenictus, and is used for low lines running from lateral portions of clypeus laterad to antennal sockets, thus separating them from the genae. Such ridges are present in most Cerapachyini, but absent in many Sphinctomyrmex, all Acanthostichus and Cylindromyrmex.

‘Lateroclypeal tooth’ is here introduced for the modification of the lateral corners of the clypeus, which in cerapachyines can be variably developed, from being bluntly pointed to drawn into conspicuous teeth that project over the mandibles.

Nomenclature

 *  CERAPACHYS [Cerapachyinae: Cerapachyini]
 * Cerapachys Smith, F. 1857a: 74. Type-species: Cerapachys antennatus, by subsequent designation of Bingham, 1903: 28.
 * Cerapachys senior synonym of Ceratopachys: Wheeler, W.M. 1922a: 755.
 * Cerapachys senior synonym of Parasyscia, Syscia (and its junior synonym Cysias): Kempf, 1972a: 76; Brown, 1975: 18.
 * Cerapachys senior synonym of Chrysapace, Lioponera, Neophyracaces, Ooceraea, Phyracaces, †Procerapachys: Brown, 1975: 18.
 * Cerapachys senior synonym of Yunodorylus: Bolton, 2003: 141, 268.
 *  ORAPACHYS [unavailable name]
 * Orapachys Forel, 1893a: 162, incorrect subsequent spelling of Cerapachys.
 * CERATOPACHYS [junior synonym of Cerapachys]
 * Ceratopachys Schulz, W.A. 1906: 155, unjustified emendation of Cerapachys.
 * Ceratopachys junior synonym of Cerapachys: Wheeler, W.M. 1922a: 755.

Bolton 1994 - Ants with the following combination of characters together.

1 Clypeus, from front to back, moderately broad to reduced; in the latter bringing the antennal sockets close to the anterior margin of the head.

2 Antennal sockets horizontal, in the plane of the transverse axis of the head, partially or wholly exposed in full-face view.

3 Frontal lobes rarely weakly present, predominantly vestigial to absent; usually narrow vertical carinae are all that are present between the antennal sockets.

4 Narrow neck joining condylar bulb of antennal scape to shaft of scape proper straight, not sharply angled or bent downwards in frontal or full-face view.

5 Eyes usually present but frequently reduced or absent in some groups; antenna with 9-12 segments.

6 Promesonotal suture usually absent (present in just one species, where it is fused and inflexible), the alitrunk fusiform and box-like.

7 Metapleural gland orifice in lower posterior corner of metapleuron, opening laterally, the orifice concealed behind a ventrally directed cuticular flange or flap.

8 Propodeal spiracle situated low down on the side of the sclerite, at or behind the midlength.

9 Metatibial glands present.

10 Metacoxal cavities closed; cuticular annulus around each cavity broad and complete, the annulus not broken medioventrally nor with a flexible suture traversing the annulus from the coxal cavity to the cavity in which the petiole articulates.

11 Propodeal lobes present.

12 Waist of 1 or 2 segments. Generally of a single, separated segment, the petiole (= abdominal segment 2); usually also with a deep constriction between abdominal segments 3 and 4. Abdominal segment 3 with a graded morphoclinal reduction from a full-sized segment to a small postpetiole, thus making the waist 2-segmented.

13 Petiole sessile to subsessile, the tergite and sternite not fused; sternite of petiole with a simple posterior margin and simple articulation to the third abdominal segment.

14 Abdominal stridulatory system absent.

15 Abdominal spiracles 5-7 shifted backwards, not concealed by the posterior margins of the preceding segments and visible without distension or dissection of the abdomen.

16 Helcium sternite large and convex, bulging ventrally, visible in profile in normally mounted specimens; tergite of helcium lacking a notch or impression in its dorsal margin anteriorly.

17 Abdominal segment 3 [Note: petiole is abdominal segment 2] with tergosternal fusion; tergites and sternites of following abdominal segments (4-7) not fused.

18 Abdominal segment 4 with presclerites sharply defined and differentiated from the postsclerites, the former fitting tightly within the posterior end of the third segment.

19 Pygidium (tergite of abdominal segment 7, the last visible tergite) large, its dorsum flattened or impressed; lateral and/or posterior margins of flattened area armed with a series or row of denticles, small teeth, or peg-like spines, with more than 2 pairs present.

20 Sting large and strongly developed.

Brown (1975, Footnote 38): The singularis group consists of large and medium-sized red ants, some with a black or fuscous gaster, that possess a well-defined carina curving from the posterior corner of the head forward toward the compound eye, which it usually fails to reach. This carina is a kind of anterior continuation of the sharp dorsolateral margins of the trunk and petiole, well developed in these species. In the small, black, forest species of the turneri group from Queensland, the posterior corner of the head may bear a blunt ridge where the sides and the cervical surface of the head meet, but this does not form a sharp carina and does not curve toward the eye.

The singularis group is still poorly known, and some of the species coming out close together in the key may well be synonyms, particularly where one form is known only from the worker, and the other only from the queen, for example, Cerapachys pictus and Cerapachys singularis. I have synonymized the "subspecies" rotula under 'singularis', because they differ chiefly in whether the gaster is red or fuscous, and this character varies even in the rotula type series.