Venice lagoon barrier leads to rodent invasion

The Pantegana is a beloved symbol of Venice’s renowned Carnival, but its real-life relatives are less welcome in the squares and alleyways of the city. Photo / Getty Images

Venice’s controversial €6 billion ($11.9b) sea defence barrier was designed to save the city from floodwaters that routinely engulfed the lagoon and swamped its squares and alleyways.

And while critics who claimed it would never work have been proved wrong, its success in keeping the floods at bay has had an unwelcome consequence – a dramatic rise in the rat population.

Rat colonies are no longer washed away and drowned in the floods, bringing to an end a natural population control that had existed for centuries.

Until the MOSE barrier was built, rats – especially newborn and young animals – would struggle to escape rising floodwaters.

Now, they survive. Female rats can become pregnant seven or eight times a year, producing litters of six to 12 babies, meaning that if left unchecked, the population increases exponentially.

Rats become sexually mature and capable of reproducing at an early age, so a single female rat can have up to 15,000 descendants in a year.

“We have seen a definite increase in the number of rodents in the city,” said Filippo Roncali, the technical manager of Veneziana Disinfestazione, a pest control company.

“In the past, when a high tide surpassed a certain threshold, the water would reach the sewers. The adult rats could escape, but the young would drown.”

The frequent sluicing out of the city’s canals, lagoons and sewers kept the rat population in check.

Chiara Delmonte, the founder of Veneziana Disinfestazione, told La Nuova Venezia newspaper: “Before the arrival of MOSE, we knew that in the wake of a high-tide event the phone would ring incessantly with reports of rats fleeing the rising waters.”

There are two types of rat living in Venice – the Norway or brown rat, and the black rat, the species believed to have spread the Black Death in the Middle Ages.

The plague, transmitted through fleas living on rats, is thought to have killed more than a third of Europe’s population between 1347 and 1351.

Rats in Venice also thrive on the food waste produced by the millions of tourists who visit the city each year, who appear to have been undeterred by an entrance charge that has been imposed on day-trippers.

According to tradition, Venice’s annual Carnival kicks off with a giant papier-mache model of a rat aboard a gondola making its way through the canals of the Unesco-listed city.

Known as the Pantegana – the local dialect word for the Norway rat – it is a long-standing symbol of the carnival.

The MOSE flood barrier, named after Moses, the Biblical figure who parted the Red Sea, became fully operational in 2023.

It consists of 78 giant hinged metal gates that can close off the Venetian lagoon from the Adriatic.

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