Platypus Facts

The platypus's strangeness runs deeper than its looks. It is a monotreme — a member of a tiny, ancient branch of mammals that lays eggs instead of giving birth to live young. Its only living relatives are the echidnas, including the short-beaked echidna. Like all mammals it has fur and produces milk, but it keeps the reptile-like trait of egg-laying, and the monotreme lineage goes back over 100 million years, which makes the platypus a living window into early mammal evolution.

The platypus's soft, leathery bill is not a duck's beak but a sensory organ packed with thousands of electroreceptors and touch receptors. A hunting platypus closes its eyes, ears, and nostrils underwater and "sees" entirely through the bill, detecting the faint electrical fields produced by the muscle movements of prey buried in mud. It is one of very few mammals that hunt this way.

Males carry a second oddity: a sharp, hollow spur on each hind ankle linked to a venom gland. The venom is not deadly to humans but causes severe, long-lasting pain, and it is used mainly in fights between rival males in the breeding season. Adult platypuses also have no teeth — they grind food between keratin pads, using grit scooped from the riverbed to help break down hard shells.

The platypus lives only in eastern mainland Australia — Queensland, New South Wales, and Victoria — and in Tasmania, and it needs permanent fresh water. It occupies rivers, streams, deep creeks, and some lakes and reservoirs, from tropical Queensland rainforest to cold Tasmanian alpine streams. Just as important as the water is the bank: platypuses need steep, well-vegetated earthen banks to dig their burrows above the waterline, with overhanging plants, submerged logs, and roots that both shelter them and support the invertebrates they eat.

The platypus is a carnivore that forages on the bottom for freshwater invertebrates — insect larvae such as caddisflies, mayflies, and dragonflies, plus worms, freshwater shrimp, small crayfish (yabbies), and snails. Its metabolism is high enough that it may eat up to 20% of its body weight a day, spending 10 to 12 hours foraging. Hunting relies entirely on the bill: diving to the bottom, the platypus sweeps its bill side to side to pick up the electrical and mechanical signals of hidden prey. Because it cannot chew or swallow underwater, it stores food in cheek pouches, then surfaces and grinds the meal against its keratin pads, using swallowed grit to crush hard shells.

Platypuses are solitary and mostly active at night and twilight, forming no lasting social bonds beyond breeding. Superb in the water, they are slow and awkward on land — walking costs them about 30% more energy than a typical land mammal its size — so they spend most of their out-of-water time resting in burrows. They dig two kinds: a simple resting burrow used year-round and a longer, elaborate nesting burrow the female builds for breeding. Usually quiet, they can emit a low growl when disturbed, and males turn aggressive in the breeding season, using their venomous spurs in fights over territory and mates.

After a brief aquatic courtship the male leaves, and the female raises young alone. She digs a deep nesting burrow — up to about 30 metres into the bank — plugging it at intervals with soil to guard against floods and predators and to hold in warmth and humidity, then lays 1 to 3 small, leathery eggs after a gestation of roughly 21 days. She incubates them curled around her body, and after about 10 days the young — called puggles — hatch blind and hairless. Female platypuses have no nipples; they release milk through pores in the skin, and the puggles lap it from the fur. The mother nurses them in the burrow for three to four months, until they emerge fully furred and able to forage. Wild platypuses can live 10 to 17 years.

The platypus is listed as Near Threatened, with populations trending downward across much of its range. Although protected in Australia, its dependence on healthy freshwater makes it very sensitive to change. Habitat loss is the biggest threat: clearing and development erode the banks it burrows into and pollute the water, wiping out its invertebrate food, while dams and weirs alter flow and temperature and cut populations off from one another.

Climate change worsens this through severe droughts that dry out rivers and strand platypuses in the path of predators such as foxes, cats, and dogs. Once hunted heavily for its waterproof fur (now banned), the platypus today also drowns in illegal or discarded nets and enclosed yabby traps.

• Australian Museum: Platypus Information
• IUCN Red List of Threatened Species: Platypus
• San Diego Zoo Wildlife Alliance: Platypus
• World Wildlife Fund Australia: Platypus Conservation