Feral Goats
Credit: Matej Ziak | Shutterstock http://www.shutterstock.com/gallery-723181p1.html

Species: Capra hircus
Origin: Western Iran
Where: Mainly a problem on small islands, especially in the U.K., the Canary Islands, Balearics, Crete, Aegean Islands, and Corsica.
When: 7,500 years before present
Why: Goats trample vegetation and overgraze, ruining available habitat for native animals and threatening vulnerable plants. Ranked 17th on the list of 100 of the world's worst invasive alien species by the International Union for Conservation of Nature.
Impact: Affects 15 threatened species in Europe.