The male platypus has a conspicuous spur located on each inner hind ankle. As shown below, adult male spurs (upper photo) are typically 15-18 millimetres long and similar in shape to a dog’s canine tooth. By comparison, the developing spurs of juvenile males (lower photo) appear to be shorter and thicker than those of older animals, due to their being covered with a protective whitish layer of keratin (the same structural protein found in human fingernails). The keratin layer chips off gradually, starting at the tip, and normally is entirely gone by a young male’s first birthday. For a detailed description of how the size and appearance of male spurs change with age, see Williams et al. (2013) or access the well illustrated guide by Grant et al. (2024): https://www.publish.csiro.au/AM/AM24020. Females (both juveniles and adults) lack conspicuous spurs, though tiny vestigial spur-like structures occur in females up to the age of about 9 months.
The spurs of mature adult males are designed to inject venom produced by paired glands (known as crural glands) located in the upper thigh (Temple-Smith 1973). Platypus venom is a clear, slightly sticky fluid containing a different suite of active compounds than those found in snake venoms (Koh et al. 2009). Although not known to be life-threatening, it causes severe pain and swelling which can take several weeks to subside, with muscle wasting and some degree of local swelling sometimes persisting for months (Temple-Smith 1973; Fenner et al. 1992). The pain is not relieved by standard analgesics such as morphine. However, it can be treated successfully using drugs which act to block nerve transmission (Fenner et al. 1992).
Platypus venom is only produced by mature males, and venom production peaks during the platypus breeding season. It is therefore believed that platypus venom delivery has mainly evolved to help males compete for mates (Temple-Smith 1973; Whittington and Belov 2007; Koh et al. 2009). A spurring response is triggered when an adult male is touched or stroked on its belly between the hind legs, especially in the mating period. The platypus’s hind feet rotate outwards and upwards, pulling each spur erect and locking it into position against the lower limb bones. Both spurs are then jabbed inwards with great force (Temple-Smith 1973).
To avoid being spurred by a platypus, never try to hold or support an adult male (or a platypus of unknown age and sex) from below. Instead, lift the animal by grasping it firmly around the end half of the tail (not the base of the tail, which can be reached by the spurs – see illustration at right). While holding a platypus in this manner, it should be easy to see if spurs are present.
Photos: APC; drawing at right by Peter Marsack
LITERATURE CITED
Fenner PJ, Williamson JA and Myers D (1992) Platypus envenomation – a painful learning experience. The Medical Journal of Australia 157, 829-832.
Grant T, Serena M, Williams GA and Temple-Smith P (2024) Age determination in the platypus (Ornithorhynchus anatinus) using spur sheath and spur developmental stages: a review. Australian Mammalogy 46, AM24020.
Koh JMS, Bansal PS, Torres AM and Kuchel PW (2009) Platypus venom: source of novel compounds. Australian Journal of Zoology 57, 203-210.
Temple-Smith PD (1973) Seasonal breeding biology of the platypus, Ornithorhynchus anatinus (Shaw 1799), with special reference to the male. PhD Thesis: Australian National University, Canberra.
Whittington CM and Belov K (2007) Platypus venom: a review. Australian Mammalogy 29: 57-62.
Williams GA, Serena M and Grant TR (2013) Age-related change in spurs and spur sheaths of the platypus (Ornithorhynchus anatinus). Australian Mammalogy 35, 107-114.