A tag for fastening to an animal's ear, the tag having a body with an opening therein and a shaft having a head portion at one end thereof, the head portion in use being passed through the ear and into the opening. In order to provide an opening in the ear of the animal which is of sufficient size to accommodate the shaft, the extremity of the head portion is provided with an annular cutting edge. In order to prevent slippage of the position of the tag against the animal's ear during initial stages of application of the tag, a locating spike is provided which projects axially of and beyond the annular cutting edge.