Procambarus clarkii, as they are properly known, are believed to have spread to Berlin’s Tiergarten park when they were released from local acquariums.
The freshwater crabs – which are considered pests outside of their natural habitat – can devastate domestic fish tanks by eating all of the plants.
Individual red swamp crayfish dumped outside the park appear to have gathered and bred.
Heavy rainfall in recent weeks may have altered the water balance or drowned the caverns in which the crawfish were living in Berlin.
The crabs are a famous part of Louisiana cuisine, with the crawfish boiled with lemon, spices and vegetables.
Strict poaching laws in Germany make it a criminal offence for Berliners to catch the crawfish and cook them – so officials are hoping foxes and raccoons will devour them instead.
“We are focusing on the natural enemies of the crabs,” said a city official.