Anguis fragilis
It forms part of the City and County of Cardiff and is now managed by Cardiff Council's Flat Holm Project Team and designated as a Local Nature Reserve, Site of Special Scientific Interest and a Special Protection Area, because of the maritime grassland and rare plants such as rock sea-lavender ("Limonium binervosum") and wild leek ("Allium ampeloprasum"). The island also has significant breeding colonies of lesser black-backed gulls ("Larus fuscus"), herring gulls ("Larus argentatus") and great black-backed gulls ("Larus marinus"). It is also home to slowworms ("Anguis fragilis") with larger than usual blue markings.