Are Platypuses Venomous? The Male's Ankle Spur Explained

Where is the platypus’s venom?

The venom system of the platypus has two parts. The first is the spur, a horn-covered, hollow spike roughly 1.5 cm (0.6 in) long on the inner side of each hind ankle. It normally lies flat against the leg but can be raised when the animal strikes.

The second part is the venom gland, called the crural gland. It sits in the upper hind leg and is connected to the spur by a duct. When a male drives his spur into another animal, the gland pushes venom through the duct and into the wound.

Young platypuses of both sexes start out with spur buds. In females these drop off while they are still young, so adult females have no spurs and no venom. In males, the spurs become fully hard and sharp as they mature.

What is platypus venom used for?

Platypus venom is not used for hunting. The platypus feeds on small invertebrates such as insect larvae and shrimps, which it finds with its sensitive bill and crushes with horny pads, as explained in How do platypuses find food?.

Instead, the venom is a weapon in competition between males. The crural gland grows much larger in the breeding season, roughly late winter to spring, and shrinks again afterward. During this time males fight over females and territory along rivers, and many adult males carry spur wounds. This seasonal pattern is strong evidence that the venom evolved mainly for male rivalry. Spurs may also help a male defend himself if he is grabbed by a predator.

What is in platypus venom?

Platypus venom is a mixture of more than 80 different toxins, according to studies of the venom gland. Many of them are proteins called defensin-like peptides, related to substances the immune system uses to fight germs. Others resemble toxins found in reptiles, which is a striking example of convergent evolution: similar molecules evolved independently in very different animals.

Researchers are interested in the venom because one of its main effects is to switch on pain pathways directly. Understanding how it does this could help scientists study how long-lasting pain works in the body.

What happens if a platypus stings a person?

People are rarely spurred, because platypuses are shy and avoid humans. Most cases have involved someone picking up a male, for example a person trying to rescue a platypus caught in a fishing line or net.

The main effect is sudden, severe pain at the wound, which spreads up the limb and is often described as far worse than the size of the wound suggests. Swelling follows. The pain can last for days or weeks, and a few people have reported increased sensitivity to pain in the area for months afterward. Some have also felt sick or faint.

The venom is not known to be deadly to people, but anyone who is spurred should seek emergency medical help immediately, by calling 000 in Australia, 911 in the US, 112 in the EU or 999 in the UK.

How to stay safe around platypuses

The simplest rule is to leave platypuses alone. They are protected by law across Australia, and only trained wildlife carers and researchers should handle them.

• Watch from the bank, quietly, at dawn or dusk, without trying to touch or follow the animal.
• Never pick up a platypus, even one that seems stuck or injured. Contact a local wildlife rescue group or park ranger instead.
• Keep dogs on a lead near platypus streams. Spurs are a real danger to dogs, and dogs can also injure or kill platypuses.

Is the platypus the only venomous mammal?

The platypus is the best-known venomous mammal, but it is not the only one. A few shrews, including the northern short-tailed shrew of North America and the Eurasian water shrew, have venomous saliva that helps them subdue prey. The solenodons of Cuba and Hispaniola deliver venom through grooved teeth, and the slow lorises of Southeast Asia mix secretions from glands on their arms with saliva to produce a toxic bite.

What makes the platypus unique is its delivery system. It is the only living mammal that injects venom through a spur rather than teeth. Its closest relatives, the echidnas, also have ankle spurs in males, but their glands produce a milky secretion that is not venomous and is thought to be used for scent signals in the breeding season.

For a wider look at venomous species across the animal kingdom, see the most venomous animals.