A green-head ant carries off a wattle seed that is specially designed to be spread by ants. The white part, called an elaiosome, is full of fat. It attracts ants who take the seed back to their nest. 
The caterpillar of an Imperial Hairstreak Butterfly, Jalmenus evagoras, and a leafhopper are tended and protected by Iridomyrmex gracilis ants. In return they supply the ants with a sugary secretion.
All ants belong to the family Formicidae and together with wasps and bees belong to the Order Hymenoptera. There are lots of different ant species. In Australia alone there may be more than 3000 different species of ants, but so far only around 1300 have been scientifically named.
Ants are social insects that live in colonies. Their colonies are perennial, meaning they survive from one year to the next. The size of a colony depends on the species of ant. They range from a few tens or hundreds of individuals to several millions.
Many people regard ants as pests. Some species come inside houses looking for food or water. A few can even live indoors, nesting in wall cavities and ceiling spaces or sometimes inside electrical appliances. Outdoors their nesting activities can destabilise paved areas and play havoc with lawns, playing fields and golf courses.
Ant stings can be very painful but are usually short-lived. However, people who are sensitive to ant venoms can suffer severe allergic reactions. In the worst cases stings can be life-threatening, but deaths are rare.
Finally, a few introduced ant species are among the worst environmental pests. These invasive species can build up in huge numbers and affect native plants and animals.
In spite of their bad reputation ants play very important roles in the environment. They are major predators of other insects and invertebrates and some are important seed feeders. Conversely, ants provide an important food source for many animals including other insects and spiders as well as many reptiles, birds and mammals.
Many species of ants nest in the ground and their excavations help to turn and aerate the soil. Their tunnelling also helps rainfall to penetrate the soil.
Some plant species have seeds that are specially designed to be spread by ants. Australia has more plant species with seeds that are spread by ants than anywhere else in the world.
Ants also form close relationships with many other animals and plants. Some plant species grow special cavities in which particular ant species nest. In return the ants attack insects and other animals that try to feed on the plant. These close relationships between ants and plants are not very common in Australia compared to other tropical countries.
The caterpillars of some butterfly species are tended and protected by ants. In a few rare cases the butterfly caterpillars live within ant nests and feed on ant larvae. Australia has more species of these 'predatory' butterflies that anywhere else in the world.
Learn more about Australian ants
CSIRO’s ‘Ants Down Under’ is an excellent site providing information on the biology, identification and distribution of Australian ants.
The Australian Ants. 2000. Their Biology and Identification. Monographs on Invertebrate Taxonomy Series Volume 3. S. Shattuck, CSIRO publishing.
Ants of Brisbane. 2007. Burwell, C.J. Queensland Museum, Brisbane. 68 pages.
Tetraponera punctulata ants gang up on a moth caterpillar. Ants are major predators of other insects.
Funnel ant, Aphaenogaster longiceps, nest entrances stand out against a burnt landscape. In many environments ants move more soil than earthworms.
This sugar ant, Camponotus eastwoodi has a waist made up of a single segment.
Although they are sometimes called 'white ants', termites are not ants at all, but are more closely related to cockroaches.
A female velvet ant belonging to the family Mutillidae. This is not an ant at all, but a wingless wasp.
The identification of ants is based on the workers. The body of a worker ant is divided into three regions:
- the head which has a pair of antennae and the mouthparts
- the mesosoma which has three pairs of legs
- the metasoma which consists of narrow waist of one or two small segments followed by a group of segments called the gaster.
Ants should not be confused with termites (Order Isoptera) another group of social insects that live in colonies. Although they are called 'white ants', termites are more closely related to cockroaches. Ants differ from termites in several ways.
Ants
- Head of workers usually with a pair of distinct compound eyes. Sometimes eyes very small and rarely eyes absent.
- Body with a distinct waist of one or two small segments.
- Antennae ‘elbowed’ with the first segment much longer than the others; segments rarely bead-like.
- Immature stages are legless, grub-like larvae that go through a pupal stage.
- Workers are all females.
Termites
- Workers and soldiers without compound eyes.
- Body without a waist.
- Antennae not elbowed; first segment not very long; remaining segments bead-like.
- Immature stages are nymphs that look like small adults; no pupal stage.
- Workers and soldiers are males and females.
There are several kinds of wingless wasps that look very similar to ants. Females wasps belonging to the family Mutillidae are even called 'velvet ants'. Ants can usually be separated from them by their strongly elbowed antennae and small waist segments.
One other characteristic feature of ants is their metapleural glands. These are found only in ants, although some species have lost them. They produce antimicrobial substances and are thought to help prevent the spread of diseases in the colony. The glands have a small opening on the side of the mesosoma just above the bases of the hind legs.
Inside the nest of the Household Sugar Ant, Camponotus humilior. The worker ants (sterile females) are tending the legless larvae. The larger white ‘bags’ are cocoons that each contain a pupa.
Some ants, like Camponotus gasseri, nest in cavities in tree branches. This species is dimorphic with two distinct sizes of workers.
An alate or winged queen of Carebara sp. within the nest. Certain weather conditions will trigger the colony to release these winged queens and winged males. The queens mate and then search for a good spot to establish a new colony.
An Iridomyrmex worker gathers sugary honeydew secreted by a scale insect. Many ant species collect honeydew from sap-sucking insects.
Ants are social insects, living in long-term colonies that survive from year to year. Most of the ants in a colony are workers. They are sterile females that collect food, tend the young and maintain and defend the nest. The ants that people see running around are almost always workers. A typical ant colony contains a single queen, the only individual that lays eggs. However, the colonies of some ant species have a few to many queens.
Ant eggs hatch into pale, legless, grub-like larvae that are fed and tended by the workers. When fully grown, ant larvae transform into non-feeding pupae that are either naked or enclosed in a cocoon. New worker ants emerge from the pupae. Worker ants are fully grown; small ants do not grow into large ants.
Depending on the species, the worker ants in a colony may:
- be all about the same size (monomorphic, eg. Green-head Ants or Spiny Ants).
- come in a range of sizes from small to large (polymorphic, eg. some Sugar Ants).
- come in two distinct sizes, small minors and large majors, with no intermediates (dimorphic, eg. Coastal Brown Ants).
At certain times of the year ant colonies produce winged ants called alates. These are reproductive females and males. They remain inside the nest until the right weather conditions trigger them to emerge. Nests of the same ant species in an area release alates at the same time. The winged males and females swarm and mate. The males are short-lived and die within a few days. Females (future queens) fly off to find a suitable nesting site, shed their wings and establish a new colony.
Many species of ants nest within the ground. Nest entrances may be in the open or located under rocks and logs. A few species are almost completely subterranean, the workers never foraging above ground. In dense forests many ants nest in the deep layer of leaf litter and many make nests in rotten wood. Other ants build their nests well above ground, using hollows in the branches and trunks of trees or creating their own nest cavities by webbing leaves together with silk produced by their larvae.
Most ants are predators or scavengers gathering a wide variety of different foods. The insect or breadcrumb that you see an ant dragging back to the nest will be fed to the larvae. In most ants the larvae only eat solid food. The worker ants themselves are liquid feeders, gathering energy rich sugary liquids such as nectar and honeydew (a sweet liquid secreted by sap-sucking insects).
Some ant species are more specialised, hunting a particular type of prey, gathering only seeds, or feeding just on sugary honeydew. Some ant species are so dependent on honeydew that they virtually farm the sap-sucking insects, often building protective shelters over them. Some ants even keep the insects in their nests during the night and take them out to feed on plants during the day.
Coastal Brown Ant
, Pheidole megacephala
Southern Meat Ant , Iridomyrmex purpureus
Bull and Jumper Ants , Mymecia spp.
Green-head Ant , Rhytidoponera metallica
Sugar Ants
, Camponotus spp.
Green Tree Ant
, Oecophylla smaragdina
Spiny Ants , Polyrhachis spp.
