Secret life of Australia's ants, the hardest workers in any backyard

Australia Broadcast Center

17-05-2025

They are builders, miners, carpenters and farmers. And despite a mostly undeserved reputation for being a stinging pest, Australian ants do an extraordinary amount of environmental heavy lifting.
While several high-profile invasive ant species — such as the red imported fire ant (Solenopsis invicta) from South America and the yellow crazy ant (Anoplolepis gracilipes) from Asia — have caused alarm due to the threat they pose to domestic agriculture and the environment, their native counterparts have quietly continued their vital, often unheralded, work.
Museums Victoria Research Institute curator of entomology Ken Walker describes a large ant colony as a "super organism" that plays an essential role in both suburban gardens and the wild.
"Ants belong to a group of insects described as 'eusocial', in that they have a large community and it's all being directed by one individual or queen," Dr Walker explained.
"They act like a single unit, so they're called 'super organisms' and they can do a lot of powerful work.
"One of the great things about ants is they dig holes in the ground, and that aerates the soil and allows water to go in.
"They also bring a lot of plant material and seeds underground, which fertilises the soil."
Of the world's 15,000 ant species, at least 1,500 are found in Australia.
By comparison, the United States has 829 species, South Africa has about 550, Great Britain has fewer than 100 species, and New Zealand has about 40.
A Proceedings of the National Academy of Sciences international study estimates the world's ant population at about 20 quadrillion (20,000 trillion).
Scientists conservatively estimate there are 2.5 million ants for every person in the world.
Ants have been part of the Australian landscape for an estimated 58 million years. During that time, they have established unusual relationships with other native flora and fauna, according to Dr Walker.
"They interact with many other insects in what are called symbiotic relationships," he said.
"There are many Australian insects, particularly butterflies, that would not survive without ants.
"In a process called myrmecochory, the female Eltham copper butterfly, for example, lays her eggs on a plant called sweet bursaria (Bursaria spinosa). If the egg was to stay there by itself, it wouldn't survive.
"The ants come up, collect the butterfly egg and take it down into their burrow. When the caterpillar emerges from the egg, the ants protect it and, at night, carry the caterpillar up to feed on the leaves.
"In return, the ants tap the caterpillar with their antennae and the caterpillar releases honeydew, which is a sweet substance the caterpillar excretes. The caterpillar gets protection, and the ant gets a source of food."
Due to their tiny brains, the intelligence of ants was often underestimated, Dr Walker said.
Ants are born with innate knowledge to do their job, but Dr Walker said there was evidence that they observed and learned from other ants to improve their efficiency.
Individual ants were also capable of remarkably complex acts of navigation and communication.
Dr Walker explained ant "scouts" use the sun's position in the sky to explore new territory and then find their way back to the nest.
"On the top of their head, each ant has three little eyes called ocelli. They use UV to know the direction the sun is," he said.
"Let's say, for example, the sun is on the right side when they go out, they know then to turn around to have the sun on their left side when they come back.
"Another interesting fact about ants is the communication … a lot of ants live underground, so they can't use visual cues, so they have to use chemical cues.
"They use a thing called trophallaxis, which can be literally defined as a kiss. Where two individuals come together, they 'kiss' or exchange a bit of fluid. In that fluid are lots of messages.
"Because each ant is kissing other ants, there's an accumulation of all the messages from the colony. Every time this kiss happens, it is gathering information of the colony.
While 1,500 ant species have been formally described in Australia, many Australian ant species are yet to be classified. Dr Walker estimated the number could be as high as 6,000.
Ant queens, males and workers often vary considerably in size and appearance, even within the same species.
These are 10 of the most commonly found worker ants in Australian backyards and landscapes:
This tiny (2-3mm) native variety is often found indoors, infesting kitchen benches while trying to get scraps of leftover food.
Superficially similar in size (2.5-3mm) and appearance to Technomyrmex but, viewed up close, has a more obvious waist and tends to be shorter and stockier.
Also called black tyrant ants or black trail ants because they form long trails as they forage for food. Workers grow up to 5mm in length. They do not have a stinger.
Perhaps Australia's most recognisable ant, growing to about 6-7mm, and featuring a dark red to purple head and blue-black body. Capable of producing huge, interconnected nests with populations up to 300,000. Very important for the environment, a meat ant nest can disperse hundreds of thousands of plant seeds while also cleaning up dead animals and controlling pests.
Also known as the banded sugar ant or carpenter ant. This familiar, relatively large (5-15mm) ant is often seen at night. These orange to black ants do not sting but some can bite with their large mandibles and spray wounds with formic acid from their rear. Despite being active at different times of the day, sugar ants and meat ants are competitive and will plug each other's nest holes with debris.
A type of carpenter ant that produces and stores its own honey. Half the workers are 5-8mm long and black, while half develop into "repletes" which swell up 17mm in length to store and distribute honey to the rest of the hive.
The Australian weaver ant is mostly orange with a green abdomen (O. smaragdina) and grows to 5-10mm. They live in trees building nests made of leaves stitched together using silk. Does not have a stinger but will bite if their nest is disturbed and spray the wound with formic acid.
Also known as the big-headed ant. There are two worker "castes", with the larger (3.5-4.5mm) ants having an oversized head and jaws, which they use to crush seeds. The smaller (2-3mm) more numerous workers transport food back to the nest.
Has a distinctive metallic green colouring, with workers measuring 5-7mm in length. It is more common in Queensland, southern NSW and South Australia, but is found in all mainland states and territories. Has a painful sting.
Some varieties are also known as inchman ants because of their length (about an inch or 25mm), or bulldog ants. Aggressive, with large jaws (mandibles) and a sting at the end of their abdomen. It is the sting, rather than the mandibles, that delivers its painful attack.
Bull ants are most common in Tasmania and south-eastern mainland Australia. They have a characteristic jumping action that can propel them up to 10cm. Generally smaller (12-14mm) than other bull ants, the Jack jumper ant has an extremely painful sting and can be dangerous and potentially fatal to those at risk of anaphylactic shock.