Platypus (Ornithorhynchus anatinus): Facts and Biology

What is a platypus?

The platypus is a monotreme, a member of the oldest surviving branch of the mammal family tree. Monotremes lay eggs, yet they have fur, are warm-blooded and feed their young on milk, which makes them true mammals. Only five monotreme species survive today: the platypus and four species of echidna, such as the short-beaked echidna. For the full story of how these unusual animals fit into the mammal group, see Is a platypus a mammal?.

The name platypus comes from Greek and means “flat foot”. The scientific name means “duck-like bird snout”. Its genus, Ornithorhynchus, has no other living species, and it is the sole surviving member of the family Ornithorhynchidae. Fossils show that platypus relatives once lived across Australia and even reached South America more than 60 million years ago, when the two continents were still linked through Antarctica.

The plural is either platypuses or simply platypus. “Platypi” is often heard but is not correct Greek or Latin.

Appearance

A platypus has a streamlined, slightly flattened body covered in short, very dense fur. The upper side is medium to dark brown, while the belly is paler, from cream to silvery gray. The fur traps a layer of air that keeps the animal warm and dry, even in cold mountain streams. Only otters are thought to have denser fur among mammals.

The bill is the platypus’s most famous feature. Unlike a duck’s hard beak, it is soft, rubbery and packed with nerve endings. The nostrils sit on top near the tip, so the animal can breathe while almost completely submerged. The small eyes and ear openings lie in a groove of skin behind the bill that closes when the platypus dives.

The front feet are broad and fully webbed, and the webbing extends beyond the claws to make powerful paddles. On land, the platypus folds the webbing back and walks on its knuckles, freeing its claws for digging. The hind feet are only partly webbed and act as rudders together with the broad, flat tail. The tail is furry, not scaly like a beaver’s, and stores fat for lean times.

Adult platypuses have no teeth. Young animals have a few small molars that they lose around the time they leave the burrow, and adults grind food between hard, horny pads instead. In 2020, scientists also reported that platypus fur glows blue-green under ultraviolet light, a property called biofluorescence whose purpose is still unknown.

How big is a platypus?

The platypus is smaller than many people expect, roughly the size of a house cat’s body without the legs. Males are clearly larger than females, and animals in the cool south, especially Tasmania, tend to be bigger than those in tropical Queensland.

Its normal body temperature is about 32 °C (90 °F), several degrees lower than the 37 °C (99 °F) typical of most placental mammals, yet it can keep warm while foraging in water colder than 5 °C (41 °F).

Habitat and range

Platypuses live only in Australia. Their range runs along the eastern side of the continent, from north Queensland through New South Wales, the Australian Capital Territory and Victoria, and includes Tasmania and King Island. An introduced population lives on Kangaroo Island off South Australia, while the original mainland South Australian population has all but disappeared.

They need permanent fresh water: rivers, creeks, lakes, farm dams and lagoon-like pools, from tropical rainforest to cold alpine streams above 1,000 m (3,300 ft). The best sites have earth banks held together by tree roots and overhanging plants, where the animals dig their burrows. You can read more in Where do platypuses live?.

What do platypuses eat?

The platypus is a carnivore that feeds on small animals living on the bottom of streams and lakes. Its main prey are insect larvae such as caddisflies, mayflies and dragonflies, along with freshwater shrimp, yabbies (small crayfish), worms, snails, small mussels, tadpoles and fish eggs.

It hunts underwater with its eyes, ears and nostrils shut, relying on about 40,000 electroreceptors in the skin of its bill. These detect the tiny electric fields produced by the muscles of moving prey, while touch receptors pick up movement in the water. Sweeping its head from side to side, the platypus probes the mud and gravel, stuffs food into cheek pouches and grinds it at the surface. Most dives last around 30–40 seconds. The full story is told in How do platypuses find food?.

Because it is small and lives in cold water, the platypus needs a lot of food, and it may spend 10 hours or more a night foraging.

Behavior and venom

Platypuses are mostly solitary and nocturnal, although they are often active at dawn and dusk and sometimes by day in winter. They rest in burrows dug into the bank, usually with the entrance just above the waterline. A home range can stretch along several kilometers of river, and the range of one male often overlaps those of several females.

They swim with alternating strokes of the webbed front feet, an unusual style among mammals. Platypuses are quiet animals, but they have been heard to growl softly when disturbed.

Adult males carry a hollow spur, roughly 1.5 cm (0.6 in) long, on the inside of each hind ankle. It connects to a venom gland in the thigh that grows larger in the breeding season, when males use their spurs to fight rivals. The venom is not deadly to people, but it causes intense, long-lasting pain. Females are born with spur buds that drop off before they become adults. Read more in Are platypuses venomous?.

Reproduction and life cycle

Platypuses mate in the water in late winter and spring, roughly from June to October, with northern populations breeding earlier than southern ones. The female then digs a special nesting burrow that can be more than 20 m (65 ft) long, lines a chamber with wet leaves and grass, and seals the tunnel with plugs of soil.

She usually lays two eggs, sometimes one or three. The small, leathery eggs are about 17 mm (0.7 in) long and have developed inside her body for about 28 days. She curls around them, holding them against her belly with her tail, and they hatch after about 10 more days of incubation.

The young are tiny, blind and hairless when they hatch. The mother has no nipples: milk seeps out through pores on two patches of skin on her belly, and the young lap or suck it from her fur. They stay in the burrow for about four months before swimming out for the first time in late summer. Females are thought to start breeding at about two years old, although many breed for the first time later.

Platypuses live a long time for their size. Many wild animals reach 10–15 years, and marked individuals in the wild have been recaptured at more than 20 years old. In captivity, platypuses have lived past 20 years.

Predators and threats

Natural predators include large goannas (monitor lizards), carpet pythons, birds of prey such as eagles, Murray cod, large eels and, in the north, saltwater crocodiles. Introduced red foxes, feral cats and dogs also kill platypuses, especially young animals or those crossing land.

The bigger dangers today come from people. Dams and water extraction change river flows, droughts dry out pools, and land clearing causes banks to collapse and streams to fill with silt. Platypuses also drown in enclosed nets and traps set for yabbies, which is why several Australian states have banned or restricted such traps. Pollution, plastic litter that can loop around their bodies and climate change add to the pressure.

Conservation status

The IUCN Red List classifies the platypus as Near Threatened (assessment 2016), with a decreasing population. Researchers estimate that numbers have fallen by about 30% on average since European settlement, and much more in parts of the Murray–Darling Basin in the southeast. The total population is unknown because platypuses are shy, nocturnal and hard to count.

The species has been legally protected in every state where it lives since 1912, after decades of being hunted for its fur. Victoria now lists it as Vulnerable under state law, and it is listed as Endangered in South Australia. Researchers have recommended a national threatened listing as well.

Myths and facts

Myth: the first platypus was a hoax. When the first preserved platypus reached Britain in 1799, many naturalists suspected that a duck’s bill had been sewn onto a mammal’s body. The zoologist George Shaw, who described the species, reportedly checked the skin for stitches. It was real, and scientists only confirmed in 1884 that platypuses lay eggs.

Myth: platypuses are part duck or part reptile. The platypus is a mammal through and through. It does share some old features with reptiles and birds, such as laying eggs and a single rear opening called a cloaca, but these are inherited from very ancient shared ancestors, not mixed in from other animals.

Fact: the platypus has ten sex chromosomes. Instead of a single X and Y pair, platypuses have five pairs of sex chromosomes, a genetic system unlike any other known mammal.

Platypuses and people

Platypuses have long been part of Aboriginal culture and stories, and many Aboriginal languages have their own names for them. Today the platypus is a national symbol of Australia, appearing on the 20-cent coin and on stamps. Very few live in zoos outside Australia, so the best chance to see one is quietly at a creek or river in eastern Australia at dawn or dusk, watching for the telltale rings on the water.