This crab is native to coastal areas of eastern Asia, but has been imported to the U.S. as well as Europe. It may hitchhike in ballast waters of ocean-going freighters and be released in new areas when that water is purged from the ship. It has been found in the Great Lakes of North America but so far appears not to have established itself. It also has been found, in some cases, hundreds of miles from the ocean in residential areas. It was first found in 1991 on the West Coast of the U.S. and in 2005 along the East Coast. As of 2012 its range in the U.S. includes the San Francisco Bay and rivers east of it, the Great Lakes, and coastal areas and tributaries from Maryland north to New York.
This invasive species is a prized food delicacy in its native areas but a serious pest in North America, where it may compete with native species of crabs for food and habitat. In aquatic habitats they hide within burrows in the substrate, leading to erosion and pollution of embankments or drainage systems. They live equally well in salt or fresh water habitats and can even survive highly polluted waters. However, while they survive in fresh water they must breed in salt water, and thus must return to the sea or brackish estuaries to continue their populations. Following their 4th or 5th year of life they migrate to these salty habitats to breed, continue onto the sea to overwinter, and then begin their trek back up the streams to freshwater habitats the following spring.
The crabs are small species that are only 3 inches wide across the back of the body, which is round in shape when viewed from above. The legs may be as long as 6 inches and are dark brown to golden yellow. The palpi are medium length and stout, with short claws that are black with white tips. On top there is a distinct depressed notch between the eyes.
Characteristicts Important to Control:
This is an invasive species that must be reported to agricultural officials if found or suspected. Control begins with efforts to prevent its introduction by managing ballast waters of ocean going vessels as well as education of people to prevent deliberate introduction.