A parent’s enthusiastic donation to a primary school’s bug collection has triggered a nationwide alert for dangerous pests known to breed like rabbits, devastate the plant kingdom and transmit the deadly meningitis virus.

US agriculture officials were combing the mid-Western state of Wisconsin and have put an alert out across America last week, after seizing three cricket ball-sized great African land snails from Nicolet elementary school in Menasha, Wisconsin.

“One of our parents got them from a relative, thought they were frightening but fun-looking, and wanted to share them with us,” said principal Linda Joosten.

The molluscs were an instant hit with the children, who crowded round their glass case. “They were fascinating, very exotic and quite unlike any other snail,” said Ms Joosten. “They move and devour vegetation very quickly because they’re so large.”

But staff were shocked a week later when they logged on to the internet to find out more about their popular guests. “I was totally taken aback. We had no idea we were dealing with creatures that could be so devastating,” Ms Joosten said.

They immediately called in agriculture inspectors.

A Miami boy smuggled three giant African land snails into America in 1966 and his grandmother turned them loose in the back garden. In seven years their numbers had grown to more than 18,000 and it took officials a decade to stamp them out, according to the US government.

Wisconsin, known as the Dairy State, appears to have become the unlikely setting for an illicit trading ring in the exotic pest, which can be a culinary delicacy. Raided pet shops and animal dealers face fines of up to $1,000, but the unsuspecting school will not be punished.

This week, an Iowa pre-school also was the centre of an investigation into smuggling giant snails.

Native to Africa but also found in Asia, the snails can produce as many as 400 eggs in a single breeding session, feed off up to 500 plant species and may carry meningitis, potentially fatal to humans, in their mucus.