A radio frequency identification (RFID) tag insertion cartridge configured for use in implanting a flexible RFID tag into a small animal using a needle-retraction implant tool. In embodiments, the cartridge includes a cartridge housing and a bevel cap. In embodiments, the cartridge housing is configured to receive a carriage portion inserted into a first end of the cartridge housing with a retractable needle extended out of a second end of the carriage portion to present the retractable needle in an extended position with the RFID tag carried within the retractable needle. In embodiments, the bevel cap has a proximal portion with a mating feature configured to mate with the cartridge housing and one or more needle capture elements configured to selectively couple to the needle in the extended position in a side-mountable manner without a direct axial force being exerted on the needle.