Biological invasions are the main cause of biodiversity loss, but they can also have serious social and economic repercussions. In Europe, over 13,000 non-native (or "alien") species have an established presence, around 1,500 of which are invasive species that have a negative impact on their surroundings. Species of particular concern are the brown rat, raccoon, red swamp crayfish, tiger mosquito, varroa mite, ragweed, and ailanthus, among many others.
