Viking longboats carried house mice to colonies in Iceland and Greenland - and their descendants are still alive today.
Scientists compared modern mouse DNA with ancient samples from mouse bones found at archaeological sites.

Shetland's 'Up Helly Aa' Viking festival: As the Norsemen conquered and colonised areas, they brought with them the pitter-patter of tiny feet - Scientists found that mice in Iceland are descended from 10th century 'hitchhikers'
Descendants of these stowaways can still be found in Iceland where DNA samples were collected from nine sites.
From Iceland, the mice continued their Viking voyages to settlements in Greenland.
However, no trace of the Norse mice could be found in Newfoundland, even though the Vikings are known to have reached the Canadian province.