Carcinus maenas, commonly known as the green crab, is a species of crab native to the coasts of Europe and northern Africa. It has a distinctive greenish shell, which can also appear brown or yellow, and typically measures about 3 to 4 inches across. This crab is known for its aggressive behavior and adaptability to various environments, including estuaries and rocky shorelines. The green crab has become an invasive species in many regions, including the United States and Canada, where it poses a threat to local marine ecosystems. It preys on shellfish and other marine organisms, impacting fisheries and biodiversity. Its rapid reproduction and ability to thrive in different habitats contribute to its success as an invader.