Module 4 - Argentine ant

Argentine ant (Linepithema humile): Recognising Argentine Ants

Argentine Ants are small, shiny, dark brown ants about 2.5 mm long.
Large numbers of ants can be seen moving in single file along ant tracks or swarming over food or where their nests are disturbed.
They are the ant species most commonly found in people’s homes in the City of Cape Town.

Argentine ant (Linepithema humile): From introduction to invasion:

Argentine Ants come from northern Argentina in South America. The climate there is subtropical or temperate with moderate rainfall.
They have spread around the world and now live on all continents except Antarctica.
They probably reached Cape Town in 1900 during the South African War in a shipment of fodder imported by the British army to feed their horses.
Argentine Ants are usually found close to people (e.g. homes, gardens, farms and picnic sites) because we create a favourable habitat for them with adequate food and water.
Argentine Ants are very successful, aggressive invaders. The ants in the Western Cape have lost their natural sense of aggression against other Argentine Ant colonies. This allows small colonies to combine to form giant “supercolonies”, which can dominate the ecosystem.

Argentine ant (Linepithema humile): From introduction to invasion:

These ants have a negative ecological impact because they displace indigenous insects. In the Fynbos, the Argentine Ant is threatening the survival of indigenous plants and animals.
- Indigenous ants collect and bury the seeds of over 1 000 different fynbos plant species. The seeds survive underground, protected from rodents and birds, until conditions are right for germination. Argentine Ants displace seed-burying ants but don’t bury fynbos seeds. They therefore reduce seed dispersal and the reproduction of many fynbos plants.
- They compete with local insects for nectar but do not pollinate the flowers they visit.
- Argentine Ants displace indigenous ants that protect the caterpillars of a number of local butterflies
Argentine Ants have a symbiotic relationship with plant pests like aphids. Ants have biting, chewing mouthparts and cannot get to the sugar-rich sap inside plants; bugs have piercing, sucking mouthparts and can tap into the sap inside the plant. Ants protect these bugs because they are able to “milk” them and drink the sweet, concentrated sap called honey-dew.
Bugs like aphids transmit plant diseases (just as mosquitoes transmit human diseases like malaria). Indirectly, by protecting these bugs, Argentine Ants help to spread plant diseases in gardens and orchards.

Argentine ant (Linepithema humile): Controlling Argentine Ants

Argentine Ants are not much of a problem in remote Fynbos areas as it is generally too hot and dry for much of the year. They require food and a moist environment, which human settlements provide.
Alien ant colonies need to be poisoned, but this must be done very carefully in order to avoid harming other animals or people. It is best to use an ant trap: worker ants have to enter the trap to fetch the poison; they take it back to the nest and feed it to the queen, killing the individual that lays the eggs.

Argentine ant (Linepithema humile)