A genetic similarity between snail fossils found in Ireland and the Eastern Pyrenees suggests humans migrated from southern Europe to Ireland 8,000 years ago.
The slimy creatures in Ireland today are almost identical to snails in Southern France and Northern Spain.
Whether an accidental visitor on a ship or brought along as a snack, the boat they were carried on did not appear to stop in Britain.
The findings are published in PLOS One.
As Britain emerged from the end of the last Ice Age about 10,000 years ago, sea levels rose and landslides are thought to have triggered a great tsunami. Britain was transformed into an island, separated from mainland Europe and Ireland.
Land-dwelling animals were therefore no longer able to migrate from Europe over the seas without a little help.
It has long perplexed scientists that Ireland has plants and animals that are genetically different, and in some cases are even unique, to ones found in Britain.
Now scientists have found that a common garden snail, Cepaea nemoralis, is almost genetically identical to one found in the Eastern Pyrenees, but seems to have missed Britain on its journey over.
Fossil analysis revealed a continuous record for these snails in Ireland for the past 8,000 years and well preserved shell remnants from France showed the creature was a snack thousands of years ago.
The researchers said it was difficult to explain this "clear pattern" except by involving humans.
"There are records of Mesolithic or Stone Age humans eating snails in the Pyrenees, and perhaps even farming them," said co-author of the study Angus Davison from the University of Nottingham.
"If the snails naturally colonised Ireland, you would expect to find some of the same genetic type in other areas of Europe, especially Britain. We just don't find them.
"The highways of the past were rivers and the ocean - as the river that flanks the Pyrenees was an ancient trade route to the Atlantic. What we're actually seeing might be the long lasting legacy of snails that hitched a ride as humans travelled from the South of France to Ireland 8,000 years ago.
"The intriguing implication is that the genetics of snails might shed light on a very old human migration event," Dr Davison added.
Human genetic link
Population geneticist Dan Bradley from Trinity College Dublin said the study showed a recurring theme that some species in Ireland had similar genetic types to southern Europe, but not to those found in Britain.
"It's consistent with the idea that almost everything we have in Ireland, that can't swim or fly, was brought here on a boat."
Previous genetic studies on humans have also shown clear links between the population of Ireland and those in Southern Europe.
"The genetic patterns in humans are there, but are much weaker. You see it in blood groups, in Y chromosomes and some diseases.
"In order to really understand migration patterns we need more ancient DNA from different species such as small mammals," Prof Bradley told BBC News.
Scientists, including Prof Bradley are now working on further studies on human remains, which over the next few years will "tell us exciting things about human migration".