By Francesco Tomasinelli

Updated 01/08/2006

Freshwater crab Potamon fluviatile is among the strangest european invertebrates. A crab that abandoned the sea to live and reproduce in small streams across forests. His ancestors were found in Asia and were later depicted in coins in ancient Mesopotamia and Greece
These Crustaceans are opportunists and can feed on a wide variety of preys in the water and even deep in the woods, where they venture at night or in rainy days. They emerge at night from their hides to hunt small creatures, like tadpoles and insects fallen into the waters. If the opportunity arises crabs are even able to capture small frogs and fishes.
Bad attitude, nocturnal habits and the size of a hand makes Potamon a difficult target for many predators. But the crabs are pretty vulnerable to pollution and habitat degradation, even if in the last years a population of these crustaceans was surprisingly found in good health even in the city of Rome, in an unpolluted area. Young crabs are more tied to water than adults. Females mate in late spring and give birth to young’s in summer. They pass the first months in the water (without any stage in the sea, as happens with most tropical forest crabs), before venturing around in the woods.

Other species of crustaceans live in freshwater habitats in Europe even if they have slightly different preferences: the shy European crayfish Austropotamobius and the aggressive and bigger Louisiana crayfish Procambarus clarkii, an invading species from United States. A series of experiments involving fights between different species (Potamom, Austrapotamobius, Procambarus) were recently carried on by the University of Florence to better understand the balance of power in European streams. The crab, with great surprise of everybody, proved superior to crayfishes of similar size, including the fearsome american invader.

Many thanks to Sara Fratini, Silvia Barbaresi, Alessio Bruni, Lorenzo Gori, Laura Calevo and Stefano Cannicci for precious informations and help.