Invasive species are organisms that are not native to an environment and can cause harm. Some of the worst invasive species include the European rabbit, zebra mussel, and ship rat, which have caused extinction of other species. Invasive insects and animals are often introduced unintentionally but then negatively impact the ecosystem by preying on native species or destroying property. Common invasive plants like purple loosestrife and tree of heaven spread rapidly and kill other plants. Invasive species cost millions of dollars to control and mitigate their environmental damage.