The yellow crazy ant (Anoplolepis gracilipes) is a highly invasive ant whose dense supercolonies dominate landscapes ecologically, displacing other insects and preying on small vertebrates as well.
Photo: April Nobile, from www.AntWeb.org
Yellow crazy ants are lanky, with very long legs and antennae. When the legs are straightened, these are longer than the head and body. The antennae are also longer than the head and body when extended.
The head is longer than wide. It lacks protruding jaws.
The ants are yellowish to brownish in colour, with the abdomen usually darker than the body.
It ranges in colour from brown to green.
The body has no spines or protrusions. It does not smell when crushed.
Crazy ants do not sting, and they are not quick to bite.
They are so named because they walk in short spurts, often changing direction, as if they are indecisive.
Workers are about 5-6 millimetres long. Photos often make them look bigger than they are.
Behaviour and location
Crazy ants have distinctive behaviours. They gather honeydew from the abdomens of sap-sucking bugs such as scales and can be seen on foliage attending these. To visit them they travel up and down trunks in orderly lines, but when foraging for insects, seeds or carrion on the ground they walk in short spurts, often changing direction, hence the name ‘crazy ants’. They drag away insects and other prey in groups.
Yellow crazy ants attack a gecko. Photo: Dinakarr | CC0 1.0
The ants can be found in a range of outdoor habitats ranging from rainforest to beach dunes, and also inside buildings and in industrial zones.
Crazy ants nest in various locations, including holes in the ground, rock piles, tree crevices, the bases of trees and under debris, mulch and leaf litter. They sometimes nest in pot plants, rock walls, pool filters and even in air conditioners and televisions. Unlike many ants they do not deposit soil around their nest entrance when this is a hole in the ground.
Yellow crazy ants are adapted to tropical and subtropical climates and are not likely to occur south of Sydney. They are currently found in Australia at many sites in coastal Queensland, in north-eastern Arnhem Land in the Northern Territory, and on Christmas Island.
The vast majority of ants have antennae and legs that are shorter than the combined head and body.
One species on which these are longer is the native green tree ant (Oecophylla smaragdina), the main ant found in shrubs and trees in coastal northern Australia, often present in parks and gardens, as far south as Gladstone in Central Queensland.
These ants have a green head and abdomen and come in castes of different sizes.
The major workers are much larger than crazy ants, about 10 millimetres long, but there are minor workers that overlap with crazy ants in size, but differ by associating with their larger co-workers. Crazy ant workers only come in one size.
Unlike crazy ants these ants bit readily and with persistence.
Green tree ants (Oecophylla smaragdina). Photo James Niland | CC BY 2.0 | Flickr
Green tree ants have long protruding jaws that create a pointed face. The crazy ant face (below left) is more rounded because the jaws are smaller and don’t protrude (below right).
Crazy ant (left) and green tree ant (right) Photos: Ken Walker | Museum Victoria and Michael Branstetter
Green tree ants weave together nests of live leaves, which they guard. Crazy ants do not have leaf nests. They are more likely than green tree ants to enter houses, and to reach high densities on the ground.
Green tree ant nest. Photo Bernard Dupont | CC BY-SA 2.0
Black crazy ants (Paratrechina longicornis) also have long legs and antennae but they are dark brown or black. They are an introduced species, probably hailing from Africa, that is now widespread in the northern half of Australia. They rate as a nuisance but not as an environmental threat.
Black crazy ants. Photo: Eli Sarnat, PIAkey: Invasive Ants of the Pacific Islands, USDA APHIS PPQ | Bugwood.org
Crazy ants cannot sting. They attack by nipping an animal and spraying formic acid into the tiny wounds created by their jaws. One or two ants cannot harm a human (unless they enter an eye). There have been instances of many ants collecting in socks and burning and irritating the ankles, and of ants in eyes causing irritation. It is safe to pick up one or two ants with the fingers, to be killed in a bottle in the freezer. Or they can be sprayed with a knockdown insecticide. Alternatively, a close up photo, if your camera is good, may be sufficient to establish identification.
Who to tell
Think you’ve found yellow crazy ants?
What to do depends very much on where in Australia you are.
If you are in NSW phone 1800 680 244 or use the online form.
In Western Australia you should email email@example.com or phone the Pest and Disease Information Service on (08) 9368 3080.
In the Northern Territory email firstname.lastname@example.org or phone (08) 8995 5039.
In Queensland, crazy ants are currently under official eradication in the Cairns and Kuranda area, Shute Harbour and Townsville.
If you are in the Cairns and Kuranda area, phone the Wet Tropics Management Authority on (07) 4241 0525. Around Townsville phone the Townsville City Council on 13 48 10. In the Whitsundays or Shute Harbour, contact the Whitsundays Regional Council on 1300 972 753.
Elsewhere in Queensland there is no one to contact because crazy ants are regarded by the state government as an established pest, found in scattered infestations along the coast that are not subject to eradication, except by private individuals controlling them on their land. There are large infestations in parts of Brisbane. They are a category three restricted pest under Queensland law, which means all citizens have a general biosecurity obligation to minimise the risk of further infestation. Landholders should endeavour to eradicate them and let their local council know.
If you are in South Australia, Victoria or Tasmania the climate is probably unsuitable for crazy ants.
Although crazy ants are tiny they can swarm in great numbers, killing much larger animals like lizards, frogs, small mammals, turtle hatchlings and bird chicks. When their numbers hit super colony levels they can have a devastating impact on native wildlife and plants, upsetting entire ecosystems.
On Christmas Island the ants have killed millions of the famous red land crabs and many robber crabs, both of which play an important role in the island’s forest ecology. Sap-sucking bugs and sooty moulds that severely damage plants and trees have proliferated under protection from the ants, further degrading the island’s forests. Numbers of native insects and other small animals have been dramatically reduced.
Overseas, yellow crazy ants nesting near seabird colonies have killed and deformed large numbers of chicks by constantly spraying them with acid.
Yellow crazy ants are a threat to agriculture in Australia’s warmer regions. By farming sugar-secreting scale insects and encouraging sooty moulds they can dramatically reduce the productivity of crops such as fruit trees and sugar cane. They pose a threat to tourism as well, because rainforests teeming with foreign ants are not what tourists come to see.
Crazy ants are also a social problem. They sometimes ruin television, toasters, microwaves and air conditioning units by crawling inside and causing short-circuits.
- The Wet Tropics Management Authority: Impacts of yellow crazy ants.
- Mackay Conservation Group: Crazy ants threaten Whitsundays.
- Parks Australia: Christmas Island yellow crazy ant program.
- NSW National Parks and Wildlife Service: Yellow crazy ants eradication.
- Invasive Species Council: Yellow crazy ants case study.