The changes IAS cause in the environment may threaten human settlements. Not only do IAS reduce the availability of environmental goods-and-services, but they may also increase the physical threats to human habitat. For example, many invasives enhance the frequency and intensity of fires. Numerous invasive grasses produce a great deal of flammable standing dead material and many resprout quickly after fires, giving them a competitive advantage over native species. This may threaten homes and other infrastructure.

Aquatic IAS may clog waterways used for transportation and enter hydropower facilities, threatening the provision of electricity.

Invasive termites damage homes and other infrastructure. Coptotermes formosanus (Formosan subterranean termite) lives in damp, woody conditions. It is native to China, but has spread around the world, including to many African countries. It not only feeds on timber in buildings but may also nest in homes and other structures (IUCN/SSC/ISSG 2004). The species is very aggressive and out-competes native termite species. The Louisiana crayfish, through its burrowing habits, can cause extensive damage to dams and reservoirs (GISP 2004).


The conversion of native biotic communities to invasive-dominated communities also has aesthetic and cultural impacts and this directly affects tourism. Some IAS directly threaten the habitat of species that are key to the tourism industry. Chromolaena odorata, for example, affects the nesting sites of crocodiles, directly placing these populations at risk. Water hyacinth, by clogging waterways, affects water-based recreational activities. Species loss also has adverse impacts on tourism. For example on the Seychelles’ Bird Island, where Anoplolepis gracilipes (crazy ant) displaced about 60 000 pairs of Sterna fuscata (sooty terns), tourism was adversely affected (CBD 2003).


The relationship between human health and IAS is complex, with patterns of human settlement, economic activities, environmental change and disease virulence, as well as the interactions between these, being crucial (GISP 2004). Where IAS pose human health threats it may place added strain on already fragile health systems.

International trade introduced the Asian tiger mosquito, which carries dengue fever, to the Americas and to Africa. First introduced in South Africa, it is now present in Cameroon, Madagascar, Nigeria, Réunion, the Seychelles, Kenya, Mozambique, Djibouti and Somalia. Increased exposure to vector diseases such as malaria, dengue fever, schistosomiasis (bilharzia) and trypansomiasis (African sleeping sickness) is associated with large development projects, environmental change such as forest loss, and human settlement. Forest loss, for example, has widened the transmission of some diseases previously restricted to wild animal hosts (GISP 2004). Trade has also spread the life-threatening bacteria E. coli in meat exports (CBD 2005).

Vibrio cholerae (Asiatic cholera) is the bacteria that causes cholera and is an IAS. Cholera is endemic or epidemic in areas with poor sanitation. Although cholera may cause mild or unapparent infections, in its extreme manifestation cholera is one of the most rapidly fatal illnesses known. It occurs in both marine and freshwater habitats including lagoons, estuaries, lakes and wetlands in association with aquatic animals. In coastal regions it may persist in shellfish and plankton. It may also be associated with algal blooms (plankton), which are influenced by the temperature of the water. Rising water temperature, through for example climate change, may increase the potential risk of this. Cholera is spread through the live food trade, and the contamination of water sources.