The snails, about 6 inches long with shells the size of a small human fist, were discovered in the man's luggage following a flight from Amsterdam earlier this month, the BBC reported Wednesday.
The snails, which the Nigerian claimed would be used for food, could have transmitted disease to snails in the United Kingdom if released, officials said.
"The vigilance of our officers at Glasgow airport has stopped these snails from entering Scotland, and possibly posing a risk to our native plants and wildlife," Murdo MacMillan of the Border Force in Scotland said.
Live animals require an import license which the Nigerian did not have, officials said, adding he was also violating bans on the importation of products of animal origin.
"I would warn travelers not to attempt to bring live animals into the U.K. without a permit, or to bring in any products of animal origin which may contain pests or diseases," MacMillan said.