1, the appearance is different: the grub midge, scientific name of saw-margined blue crab, is a pike family, blue crab genus crustaceans. Magnetic midge is slightly smaller than the blue crab, the chelicerae are slender, the color of the carapace is lime green, there are 4 teeth protruding from the forehead, and there are 9 serrations on the front side edge; while the blue crab has a larger body, the chelicerae are stout, there are 6 teeth protruding from the forehead, and there are 9 serrations on the front side edge.

2, different growth environments: the grub midge is a saltwater crab, while the blue crab is a freshwater crab; the grub midge grows in the near sea, mainly feeding on small animals such as small fish and shrimp and snails, and its meat is fresh and nutritious; while the blue crab lives in freshwater environments, mainly feeding on small fish and shrimp, and its meat is very tasty as well.