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The platypus is one of only three mammal species that lay eggs. It swims with webbed feet and tracks prey with its bill. The duckbill platypus’ webbed and clawed feet, sensitive bill, and paddle-like tail equip it for a highly aquatic lifestyle. A gland in each hindleg produces venom and is connected by a duct to a hollow spur at the ankle. This spur is erected to inject the venom. Only males possess the spurs. Millions of tiny, jelly-filled pits line the pliable bill. When swimming, the platypus closes its nostrils and uses the pits to sense minute changes in electric fields. The bill does not contain teeth. Ear slits lie behind the eyes. The platypus swims with its eyes and ears closed using electrical senses to find its way. It has webbed forefeet that are used for swimming. When the platypus needs to walk or dig, the webs turn back to reveal broad nails. His tail is used as a rudder when swimming and also acts as a major fat storage organ.

The platypus is found throughout eastern Australia and Tasmania. It is common wherever there is water year round, with soft, muddy banks for digging its burrow home. It is found in rivers, streams, and lakes but isn’t confined to pure freshwater. Platypuses have even been found in sewage polluted rivers.

The platypus mates in the spring. Like all mammals, the female produces milk from mammary glands. Unlike other mammals, however, she doesn’t have nipples, so the young nudge her flanks to coax milk from her ducts. In late summer, after 17 weeks of life underground, the young are ready to leave the burrow, seek a fresh home range, and pursue an independent life.

The platypus hunts mainly at dawn and dusk. It feeds on insect larvae, as well as worms, crustaceans, fish, tadpoles, and adult frogs, finding most of its prey on the riverbed. While hunting, the platypus closes its eyes and ears and navigates by touch alone. Its bill is covered with tiny, jelly-filled electrical receptors. As it probes the riverbed, it detects tiny electrical charges produced by the muscle activity of its prey. Young have teeth for a brief time but adults are toothless. A platypus uses two hornlike plates at the back of its bill to crush food; grit and sand kept in the cheek pouches help this process.

The male platypus is one of the few mammals that produces venom. Hindfeet, claws, or spurs can deliver a dose of venom that is agonizing to a human and can kill a dog. Scientists believe the spurs are mainly used in fights between males for females. Such dangerous weapons may help males avoid unnecessary competition by forcing them to keep their distance.

Persecuted by fishermen and hunted for its fur, the platypus was close to extinction in the 19th century. It has since gained protection and has recovered to a degree, but its habitats are coming under increased pressure from human activities.