Mice hitched a ride with Vikings to mount their own invasions in the 10th century, research has shown.
A genetic study shows that Viking longboats carried the weeny Norse warriors to colonies in Iceland and Greenland.
Scientists compared modern mouse DNA with ancient samples from mouse bones found at archaeological sites.
The analysis showed that the house mouse, Mus musculus domesticus, hitched lifts with Vikings in the early 10th century from either Norway or the northern British Isles.
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.
The researchers focused on mitochondrial DNA which is housed in battery-like powerplants in cells and only inherited from mothers. It can be used by scientists to trace maternal lineages far back in time.
Study leader Dr Eleanor Jones, from the University of York, said: "Human settlement history over the last 1,000 years is reflected in the genetic sequence of mouse mitochondrial DNA. We can match the pattern of human populations to that of the house mice."
Colleague Professor Jeremy Searle, from Cornell University in the US, said: "Absence of traces of ancestral DNA in modern mice can be just as important. We found no evidence of house mice from the Viking period in Newfoundland. If mice did arrive in Newfoundland then, like the Vikings, their presence was fleeting and we found no genetic evidence of it."
The research is published in the online journal BMC Evolutionary Biology.