Alien species are organisms (plants and animals, but also fungi, bacteria and viruses) introduced by humans outside their natural range, either intentionally or accidentally.

Some of them succesfully estabilish and thrive in the new environment, having negative impacts and becoming invasive.

It is these invasive alien species (IAS) that pose serious threats to the survival of many native species and are among the main causes of biodiversity loss. They also can have serious social, economic and human health consequences.


The water hyacinth, freshwater plant originating from the Amazon River basin and introduced in Europe as ornamental plant for ponds and small rivers, is a classic example of invasive alien species. Nowadays this plant is in fact expanded in many waterways, lakes and ponds at the expense of native aquatic plants and it is causing big problems to irrigated networks, hydroelectric and purification plants, navigation, fishing both amateur and professional.

The tiger mosquito is perhaps, among the animals, the best known case of invasive alien species. Originating from South-east Asia, it has been introduced accidentally in several European countries between the ‘70s and the ‘90s and since then it has spread uncontrollably throughout Europe. The Tiger mosquito’s bites, as we have all experienced on our skin, are very annoying and they cause sometime strong allergic and inflammatory reactions in very sensitive people. This species is very interesting from the health point of view, being responsible of the diffusion of chikungunya virus in 2007 and probably of the zika virus in very recent years.