Up till now the Baltic has been regarded as a haven against shipworm.

Traditionally, shipworms have avoided the Baltic Sea due to its lower salt content. The Baltic therefore holds a number of archaeological finds featuring wrecks of wooden ships and structures which would not likely have survived were it not for the mild salinity levels of Baltic waters.

This is one of the reasons why it was possible to find the royal warship Wasa and other large wooden vessels in such excellent condition after centuries at the bottom of the sea,” explains Carl Olof Cederlund , professor of marine archeology at Södertörn University College in Stockholm.

It remains to be determined just how shipworm has managed to get a foothold in the Baltic. It may have been brought in with water of higher salinity that penetrated the Danish Belts, in connection with storms, for example. It may also be that shipworm from other marine areas has been carried onboard vessels into the Baltic and released with ballast water there.

Medieval treasures
Around 100,000 well-preserved ship wrecks are scattered across the bottom of the Baltic Sea.

But the Teredo navalisspecies of shipworm, one of 65 varieties found throughout the world, has recently been making its way into the Baltic Sea, having been spotted along both the Danish and German coasts in the southern Baltic.

It was also recently found in wooden supports at the Ribersborg cold bath house in Malmö, further evidence that maritime artifacts are under threat.

Not really a worm
Shipworms are not actually worms but saltwater clams with much reduced shells. They are notorious for borrowing into and gradually destroying wooden structures in saltwater; earning the nickname “termites of the sea”.