Hairy crabs in China began to "immigrate" to Europe as early as 1900. 19 12 years, this kind of hairy crab endemic to China was first reported in Germany. 1933, German scientists believed that hairy crabs "migrated" from China to Europe through ballast water of merchant ships. This "eight-legged warrior who eats everything" began to run rampant in European rivers, posing a serious threat to the survival of native species, thus becoming the only freshwater crab species in Germany. In the midsummer, the mature hairy crabs living in the waters such as the Elbe River began to migrate in a "carpet-like" way, and traveled thousands of miles to the North Sea to prepare for the breeding in the next spring.