Cerapachys

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).

Identification
Within Australia, Cerapachys can be separated from Sphinctomyrmex (the only other genus of the subfamily known from Australia) 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.

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

Nomenclature
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, C. pictus and C. 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.