Abstract: An animal eartag houses a passive electronic transponder for use in the identification of the animal by a low frequency radio wave reading system. The eartag is formed of a generally flat and flexible plastic body or carrier member that includes an ear attaching arrangement at the upper portion thereof, and a hollow half cylinder shaped bubble or elongated first cavity at the lower portion thereof. This first cavity is closed at one end and is open at the other end. A rigid plastic insert member comprises a mating half cylinder shape that is dimensioned to closely fit into the open end of the first cavity. The insert member includes an elongated bore, or second cavity, that extends generally coaxially of the insert member's half cylinder shape. This second cavity extends less than the entire axial length of the insert member, so as to form a second cavity having an open end.