The dreaded wood-eating shipworm is invading northern Europe's Baltic Sea. The animal threatens to munch through thousands of Viking vessels and other historic shipwrecks, scientists warn.

Shipworms, which can obliterate a wreck in ten years, have already attacked about a hundred sunken vessels dating back to the 13th century in Baltic waters off Germany, Denmark, and Sweden, reported study co-author Christin Appelqvist.

Why shipworms are suddenly able to spread there remains a mystery, but studies suggest rising sea temperatures have something to do with it. In warmer water the animals, Appelqvist said, appear to be somehow "less stressed" by low salinity.