The platypus, an egg-laying mammal native to eastern Australia, is known for its unique features, including a duck-like bill and a beaver-like tail. Male platypuses possess venomous spurs, a surprising characteristic among mammals. This specialized defense mechanism sets them apart.
Anatomy of the Stinger
The platypus’s venom-delivering structure is a spur located on the inner side of each male’s hind ankle. These sharp, tooth-like spurs, typically 15-18 millimeters long, connect to venom-producing glands. The crural glands in the upper thigh produce the venom, which travels through a thin duct to the hollow spur. Female platypuses and juveniles are born with rudimentary spur buds, but these do not develop into functional venomous spurs and typically fall off before their first year. The spur attaches to a small bone, allowing it to articulate and move at a right angle to the limb, providing a greater range of attack than a fixed spur.
The Venom and Its Impact
Platypus venom is a complex mixture of peptides and other components. While not lethal to humans, it causes excruciating pain that can incapacitate a person. Swelling rapidly develops around the wound and can spread, with the pain evolving into long-lasting hyperalgesia—an increased sensitivity to pain that may persist for weeks or even months. The severe pain often does not respond to conventional pain relief, including morphine; nerve blocks may be required for effective management. Unlike snake venom, platypus venom does not appear to have a necrotizing component, though some muscle wastage has been observed, likely due to the inability to use the limb while the venom’s effects persist.
Evolutionary Role of the Stinger
The primary role of the platypus’s venomous spur system is believed to be male-on-male competition, particularly during the breeding season. Venom production significantly increases during this period, supporting the theory that it serves as an offensive weapon for asserting dominance and controlling territory. When provoked, an adult male platypus can trigger a spurring response, rotating its hind feet outwards and upwards, locking the spur into position, and then jabbing it inwards with considerable force. While its main function appears to be intraspecific combat, the venom may also serve a secondary purpose in defense against predators such as crocodiles, Tasmanian devils, and raptors. This unique venom delivery system represents an ancient mammalian characteristic, with similar spurs found in many archaic mammal groups, suggesting the platypus inherited this trait from its ancestors.