Giant Crabs Living in Roman Ruins

This took naturalists by surprise: guess who survived throughout the rise and fall of Rome's empire in the mighty ruins of Trajan?

A freshwater crab, Potamon fluviatile, proved the most persistent, thriving in the canals built by the Etruscans about 3,000 years ago.

"The ancient ruins of Trajan's Forum in the heart of the Eternal City have provided the ideal habitat for the crustacean, which is much larger than its counterparts in lakes and rivers," said Massimiliano Scalici, an Italian zoologist.

The narrow canals that flow under Trajan's Forum pour their content to the Cloaca Massima, Rome's ancient sewage system built in the 6th century BC to initially drain several marshes.

"Early results of a genetic analysis that we are doing show that the genes of the crabs at Trajan are very close to those of Greek freshwater crabs. So it's very likely that they were introduced by the Greeks 2,500 or 3,000 years ago, which means they were here even before Rome was founded in 753 BC," said Scalici.

While other crabs of the same species grow up to 5 cm (two inches), the ruins' crab can reach over 8 cm (three inches).

"Once we found a moult (shed exoskeleton) measuring 12 centimetres! Gigantism is one animal response to isolation, and it is a phenomenon that requires a long time. The hardy crabs have also shown extraordinary adaptation in a habitat that "is obviously very different" from that inhabited by their cousins in nature," Scalici said.

"Rome's crabs have a longer life expectancy at 15 years instead of 10 to 12," he noted.

Still, the crabs were first observed just 10 years ago by Scalici and another zoology student. They found a specimen minding its own business under a stone in Trajan's amphitheatre, built in 113 when the Roman Empire reached its peak.

A team at the University of Rome III started to investigate the only known colony of freshwater crabs living amid the noise and pollution of a large city.

"We think there are about 1,000 of them, but it's hard to say because we can't mark their shells, given that they shed regularly. The researchers are considering fitting specimens with microchips under their shells, but they are expensive," said Scalici.
"The crabs have very few predators, since stray cats, a frequent sight at Roman ruins, aren't interested, and gulls don't come at night because the site is lit up all the time. As for their diet, the omnivorous crustaceans feed on algae, insect larvae and snails, as well as the occasional cigarette butt and fast-food container," Scalici said.

These crabs burrow galleries of several meters below the ruins. Even if they have stood through the millennia, the biologists are worried that the crab colony could be disturbed by the work on a new subway line, reaching the proximity of the Forum's foundations.