photo from US Geological Survey (public domain)

According to a BBC News report from May, rats are the top invasive species in Europe. This should come as no big surprise as the crafty, rapidly multiplying rodents are everywhere and seem to thrive in any environment that contains people. The more people, the more rats.

Surprisingly however, they haven’t even been in Europe for that long.

The brown rat (Rattus norvegicus) is found across Europe in all habitats except high mountain ranges. It was believed to have been introduced in the 18th Century as maritime traffic increased.

–BBC News

Brown rats muscled out native rodent species, but also birds and aquatics. They also caused significant economic damage by eating crops and food stores as well as damaging buildings. But perhaps rats are considered a lost cause because they are just so good at surviving.

Ireland has its fair share of rats and other invasive critters such as feral ferrets, North American grey squirrels, and even a type of duck. There is also concern over wild boars and deer.

However, a recent piece in the Irish Times, entitled ‘They came from beneath the water’, suggests a growing concern about aquatic non-native species and their effects on the local environment.

One invasive species – the Asian clam – has spread throughout continental Europe since it was first spotted the 1980s and is now showing up in Irish rivers, where it disturbs the ecosystem by fouling riverbeds. It has also been the cause of clogged pipes in American nuclear power plants, so it isn’t a clam to be trifled with.

Controlling the spread of the “invader” is very difficult. The innocuous-looking mollusc has a yellow-green shell, grows to a length of about 5cm and breeds prolifically – a self-fertilising adult can produce up to 100,000 offspring in just a few years.

–Irish Times

It is not known how the Asian clam arrived in Ireland or why, but there is speculation that it was introduced as a food source.

Other threats to Ireland’s biodiversity include ornamental plants that have escaped from their gardens and ‘gone wild’. Not exactly alligators running amok in New York sewers, but there you have it.

Additional resources:

Invasive Species Ireland – Most Unwanted list

Ireland National Biodiversity Data Centre – National Invasive Species Database