Aphaenogaster

Notes on Australian species: The distinctive nests of Australian Aphaenogaster ants are often the first indication of their presence. These nests can be very dense and when in sandy soils, individual entrances can be large, deep cones or bores (up to 4 cm in diameter and 30 cm deep) with large mounds of loose dirt. This style of nest has resulted in these ants being known as "funnel ants." In some cases nests can be so dense and extensive that they severely affect soil structure, resulting in a loose and fragile surface which easily collapses under foot. When this occurs in situations such as golf courses, pastures and unsealed airstrips damage can be severe and these ants can become a serious problem. Although not aggressive, workers will defend their nests when disturbed, emerging from entrances in small numbers to attack intruders.

While nests can contain large numbers of workers, few workers are usually seen on the surface, and then most are found near the entrance; they are rarely seen foraging any distance from nests. It is known that these ants tend aphids on the roots of plants and that arthropod fragments are often found in the upper portions of their nests. It is possible that the tended aphids provide much of the food needed by the nest, and that the funnel-shaped entrances act as traps for surface foraging arthropods. These factors may combine to reduce or eliminate the need to forage on the surface of the ground.

Identification
Antennae are 12 segmented (including the scape) with a 4 segmented club. In side view the propodeum is depressed below the level of the pronotum and forward (anterior) section of the mesonotum, these two regions being connected by the steeply sloping rear (posterior) section of the mesonotum. All workers from a nest are approximately the same size (monomorphic).

Aphaenogaster is most often confused with Pheidole or possibly Pheidologeton. They can be separated from Pheidole by the 4 segmented rather than 3 segmented club and larger body size (over 3.4mm long), and from Pheidologeton by the 12 segmented antennae (they are 11 segmented in Pheidologeton). Additionally, both Pheidole and Pheidologeton have major and minor workers (Pheidole is dimorphic, Pheidologeton polymorphic) while Aphaenogaster has only a single worker caste (is monomorphic).

The Australian species of Aphaenogaster show differences which are little more than variation on a theme. This is in contrast to the nearby Papua New Guinea fauna where morphological variation is considerable. This difference suggests that the Australian fauna is composed of closely related species while that of PNG consists of several more distantly related lineages.

Regional Lists
Papua New Guinea Aphaenogaster