The American bullfrog ("Rana catesbeiana" or "Lithobates catesbeianus") is a semi-aquatic frog. It belongs to the family Ranidae, or 'true frogs'. Bullfrogs are native to most of North America, Canada and Mexico. The ones that live in northern America hibernate during winter. However, bullfrogs in southern US states are active all the time. Bullfrogs have been seen in South America, Asia, Western Europe and the Caribbean. These bullfrogs were brought on ships. Many people, including pet owners, have placed bullfrogs outside of their native area. They have done this: on purpose because they no longer want them, to control the pest population, or by accident by catching them in fishing nets.