A species of fresh-water crabs (Potaman fluviatile) is to be found in Italy in rivers from Sicily to Tuscany but they are becoming rare, or so it was thought. Now three zoologists, Massimiliano Scalici, Daniele Macale and Giancarlo Gibertini, who work at the Roma 3 university, have discovered that a colony of these crustaceans can be found in Trajans market in the historic centre of Rome. The crabs live a perilous existence in holes in the stones, surrounded by cats, rats, seagulls and pigeons. Their water source is artificial drainage channels, not a natural river. This isolated community shows signs of evolution and the crabs are growing larger than is normal for the species.