(Related: "51 Headless Vikings Found in English Execution Pit?")

The sea's cool, brackish waters have for centuries protected the wrecks from the wormlike mollusks. But now global warming is making the Baltic Sea (map) more comfortable for the critters, a new study speculates.

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.

"Since 1990 there has been a big range expansion in the southern Baltic," said Appelqvist, a marine biologist at the University of Gothenburg