When an organism is transported by man far from its original place, it is artificially introduced in an environment where it had not been present before and where it would not have gone autonomously, this organism can spread uncontrollably (fostered by the absence of natural enemies and mechanism of environmental self-regulation) becoming a full-fledged “alien”. An invader capable of carving out a space at the expense of other species. This process has increased during the last decades due to the movements of goods and people and it has worsened because of the rise in temperatures which facilitate the introduction of many tropical species in temperate climate zones. The spread of the alien species has become one of the most obvious signs of the world’s current ecological imbalance.
