Here in South Africa our three most problematic species of ants are the pharaoh, black ant and garden ant. There are approximately 550 other species, but these are not as problematic. The pharaoh ant is polygynous (they can have many queens in their colonies allowing them form new colonies at a rapid rate). For this reason theses ants are difficult to eradicate as they will have small, hard to detect nests that can divide, relocate and re-populate when needed.
The black sugar ant prefers to live and forage for food in suburban areas, this is what makes it a particularly problematic pest. The black sugar ant will have thousands of workers active at any given time. These ants will be found in every area around the house on the search for food. Complete elimination of this species is near impossible as they are so wide spread and breed at a very fast rate.
The garden ant, as the name suggests, is predominantly found outside in the grass and garden bed areas. This type of ant is a problem for some gardeners. They will farm aphids and scale for the honeydew they excrete, bringing them from host plant to host plant spreading these other garden pests to new, healthy plants. The ants will also eat ripe fruits, especially fruits like strawberries that lack a thick protective skin.