Platypus

The platypus (Ornithorhynchus anatinus) is found in inland waterways along the eastern part of Australia. The mature male has a spur on the inside of each rear leg. The spur is attached to venom glands on the flanks. The size of the venom glands varies seasonally, being largest in the breeding season. The purpose of the spurs is unclear, but is presumed to be related to breeding activity.

The spur venom contains a number of enzymes which cause severe local pain as well as local tissue damage. In experimental animals, it has caused death by respiratory failure and paralysis. In human victims, severe pain and swelling with loss of function of the limb may last for several days. There is no specific treatment for platypus stings. Analgesia is usually required. Tetanus prophylaxis should be undertaken according to the patient's immune status.

Australia's other monotremes, the echidnas, also possess vestigial venom glands and spur apparatus, but these are not functional.