An animal tag comprising, a penetrating component (3) having two ear penetrating members (9) joined by a strip of intermediate material (13), a complementary component (5) having a locking portion (17) for each penetrating member (9), and ramp means (21) for each locking portion (17), wherein the penetrating members (9) are designed to be passed through the ear of an animal and to lock onto the locking portions (17) to sandwich the ear in a gap between the penetrating component (3) and complementary component (5) and the ramp means (21) co-operate with the ear penetrating members (9) to vary the size of the gap whereby to provide a range of gap sizes to accommodate varying ear thicknesses and/or growth of the animal.