Tandonia sowerbyi is a species of air-breathing, keeled, land slug, a shell-less terrestrial gastropod mollusk in the family Milacidae.

[1][2][3] This is a keeled slug attained 80 mm (3.1 in) in length.

[3] This slug occurs in open habitats such as grasslands and shrublands; it can be abundant in arable land and gardens.

[1] It is now widespread in southeastern and Atlantic Europe:[1] It is also present in:[1] This species has not yet become established in the USA, but it is considered to represent a potentially serious threat as a pest, an invasive species which could negatively affect agriculture, natural ecosystems, human health or commerce.

Therefore it has been suggested that this species be given top national quarantine significance in the USA.