Overview
The foraging habits and degree of specialisation of ants vary considerably. Mostly, they are opportunistic generalists, preying on or foraging for any available food source. Such an omnivorous diet may include seeds, nectar, arthropod prey, carcasses, and carbohydrate rich exudates from specialised plant nectaries or honeydew from plant-feeding insects such as leafhoppers or aphids (Hemiptera) or lepidopteran caterpillars. However, there are more specialised species whose nutritional requirements are obtained primarily or exclusively from seed harvesting, farming other insects or fungi, or as predators of particular invertebrate species. Ants are often a dominant insect group in many terrestrial habitats thus playing a key role in the functioning of ecosystems. They are important in the seed dispersal of many plants via seed collecting, they aid the maintenance of soil health and fertility and, as largely general scavengers and predators, they are integral to the regulation of many arthropod populations. In addition, they are a vital food source for many invertebrate, bird, reptile, and mammal species. Because of their ecological importance, the use of ants as tools for
environmental monitoring
has been developed over recent years.
Diagnosis
While ants are one of the most familiar insects and can be reliably identified by even the youngest naturalist, what exactly is it that makes an ant an ant? There are several traits which will separate them from other insects. First, all ants have either a single small, distinct segment, the petiole, or two small segments, the petiole and postpetiole, between the mesosoma and gaster. For definitions of these morphological terms see the next section as well as the Glossary. These separate segments are absent from almost all other insects other than a few groups of wasps. A character which is found only in ants is the metapleural gland. This gland is found on the side of the propodeum just above the hind leg and has a small opening to the outside of the body. It should be noted that while this gland is found only in ants, not all ants have a metapleural gland. A few genera in the subfamily Formicinae have lost the metapleural gland and its associated opening.
In addition to these two characters, there are several other distinctive traits of ants. One is their elbowed antennae. The first segment of the antenna, the scape, is much longer than the remaining segments, the funiculus, and the joint between them is highly flexible. During normal activity the scape is held upright and near the head with the funiculus projecting forward in front of the body. This arrangement allows the tips of the antennae to be positioned near the mouthparts to assist in inspecting nearby objects, or to be extended forward away from the body to investigate more distant objects. While a sting is present in many ants, it is absent in several large and common groups and is of little use in separating ants from many other insects.
Description
Ants are among the most conspicuous and easily recognised of all insect groups. They range in size from small to large (2- 30 mm) and can be identified by their distinctive nodiform waist, small eyes, and elbowed antennae, and are characterised by having highly developed
social
colonies comprising large numbers of wingless sterile workers and fewer winged reproductives.
Distribution
Australia has a very rich ant fauna with around 1300 described (and many more undescribed) species, while New Zealand has only approximately 40 described species. Commonly encountered genera include
Myrmecia
(bulldog ants and jumping jacks),
Iridomyrmex
(meat ants),
Camponotus
(suger ants) and
Pheidole
(big-headed ants). A notable species is
Nothomyrmecia macrops
(the dinosaur ant) which is considered to be one of the most primitive living ants, sharing many characteristics with fossil ants from over 60 million years ago. Australia also has several
introduced
pest species including the Argentine ant (
Linepitherma humilis
), red imported fire ant (
Solenopsis invicta
) and the yellow crazy ant (
Anoplolepis gracilipes
) that have the potential to significantly impact on native fauna and flora.
Keys to and information on the biology of Australian ant genera can be found in Shattuck (1999) and
Australian Ants Online
.
Further information about the Formicidae can be found in Beattie 1985, Bolton 2003, Brothers & Finnamore 1993, Holldobler & Wilson 1990, Taylor 1991 and Shattuck 1999.