Pet stores in Maine faced special inspections while pet stores in North Carolina received letters asking them to notify state authorities if they suspect they have giant African land snails-snails that are harmful to plants and people alike.

The snail search intensified after authorities seized specimens in Illinois, Iowa, Wisconsin, Ohio, Michigan and Pennsylvania in recent months. The U.S. Department of Agriculture has confiscated more than 4,000 of the illegal snails from schools, pet stores and private breeders.

The snails have voracious appetites that pose a threat to more than 500 species of plants, including most varieties of beans, peas, cucumbers and melons. They also pose a health risk to humans because their mucous can transmit a rare type of meningitis.

It is illegal to import giant African land snails into the United States without a permit.