The Green Crab (Carcinus maenas) is a small, invasive species of crab native to the coasts of Europe and northern Africa. It has a distinctive greenish shell, often with darker spots, and can grow up to 4 inches wide. Green crabs are known for their adaptability to various environments, thriving in both saltwater and brackish habitats. These crabs are considered a threat to local ecosystems, particularly in North America, where they have spread rapidly since their introduction in the 1800s. They compete with native species for food and habitat, impacting local fisheries and marine biodiversity.