What Are the 5 Mammals That Lay Eggs?

Learn about the amazing monotremes, mammals that lay eggs and are found only in Australia and New Guinea.

Close up of short-beaked echidna walking

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The following creatures all share a unique characteristic. They are mammals that lay eggs and feed milk to their babies (or puggles as they're known). In the scientific world, this is called a monotreme; the two other types of mammals — placentals and marsupials — reproduce through live births. Only five species of animals share this extraordinary egg-laying trait: the duck-billed platypus, and four echidna species, the western long-beaked echidna, eastern long-beaked echidna, short-beaked echidna, and Sir David's long-beaked echidna.

Monotremes are only found in either Australia or New Guinea. They are all quite elusive, so little is known about their daily habits and mating rituals. The echidnas, who use their fur as camouflage, spend most of the day hiding in fallen trees or empty burrows. Most of their activity happens at night when they dig for ants, termites, and other small invertebrates using their highly adapted sense of smell. Rivers and waterways are the natural habiat for the platypus, which is also nocturnal. They can spend over 10 hours a night hunting for food which consists of small animals like shrimp and crayfish.

What Are Monotremes?

Monotremes are mammals that reproduce by laying eggs. Their name comes from Greek and means "single opening," which refers to the fact that they have only one opening for both reproductive and waste removal purposes.

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Duck-Billed Platypus

Platypus (Ornithorhynchus anatinus)

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With its distinct duck-like bill, this fascinating creature is found in Tasmania and Australia. The streamlined design of their bodies allows them to move gracefully in and under the water, where they live most of the time. Interestingly, they can produce venom from the spurs in their feet. While it can harm smaller animals, it will not kill a human.

Platypuses feed on small aquatic animals and locate their food by using their highly sensitive snouts. They often travel along the bottom of a riverbed and dig through the sediment in search of things to eat. These animals are ready to mate at two years of age and often have more than one partner in their lifetime. When the female prepares to lay her eggs, she goes off to a secluded den by herself to wait out the process. She will typically only lay one to three eggs.

A baby platypus, known as a puggle, is hairless and about the size of a human hand when it's born. It will nurse with its mother in a protective pouch for a few months and eventually get moved to a burrow as it grows older. By 4 or 5 months old, the baby is ready to learn how to swim.

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Western Long-Beaked Echidna

Wild echidna in the woods

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The western long-beaked echidna (Zaglossus bruijinii) is an unusual animal found in New Guinea. They are the largest of the monotremes, weighing in at nearly 40 pounds.

Earthworms are their main dietary staple, and they have three strong, sharp claws which they use to dig and for protection — although these animals are quite submissive and would be more likely to curl up in a tight ball to protect themselves than engage in an attack.

Mating season occurs one month during the summer, and it is usual for a female echidna to have only one offspring. Sadly, illegal poaching and destruction of native habitats have led to a decline in its population. Today, the western long-beaked echidna is considered critically endangered.

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Eastern Long-Beaked Echidna

Close up of an echidna digging for food in tree trunks

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Like their western long-beaked relatives, these eastern echidnas are much larger than the other monotremes. They are brown or black and don't have a tail, and their extremely tiny mouth sits at the very tip of their snout.

Eastern long-beaked echidna use their sizable snout to follow scent trails and root through mud and dirt for food. They are mostly nocturnal and spend the nighttime hours hunting for insects, larva, and earthworms. Since they're so elusive, little is known about their reproductive cycle, but breeding probably occurs around April or May. The eastern long-beaked echidna is considered vulnerable by the IUCN.

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Short-Beaked Echidna

Close up of short-beaked echidna

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Sometimes called "spiny anteater," the furry brown coat of a short-beaked echidna is covered in dozens of spiny quills, giving it the appearance of a hedgehog.

Because they have no teeth, their sticky tongue is used to catch termite ants and smash them inside their mouths. Short-beaked echidnas have an excellent sense of smell, which comes in handy when searching for potential mates during breeding season. It takes between 20 and 30 days for the female to gestate and lay an egg. The hatchling will live in a small pouch hidden in its mother's fur and nurse for several weeks until it's old enough to survive without her protection.

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Sir David's Long-Beaked Echidna

Young echidna under a fallen log

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Named for historian and naturalist, Sir David Attenborough, this echidna is found in New Guinea. It's the smallest of all the echidna, and sadly has been on the critically endangered list for quite some time.

Like other echidnas, it has small spurs on its hind legs that can be used when in danger. Typically they are solitary, nocturnal creatures that spend most of their life alone, but once a year they come together for mating season. During the gestational period, the female creates a well-insulated den or burrow in preparation for the egg. After the baby has grown spines and fur and has nursed enough to grow bigger, it, too, will go on to live alone. Their lifespans are quite long and a few documented monotremes in captivity were recorded to have lived 45 to 50 years.

According to the IUCN's Red List, Sir David's long-beaked echidna is critically endangered.

Why This Matters to Treehugger

Understanding the lifecycles and behaviors of monotremes is key to protecting biodiversity and their habitats. We hope that the more we all know about these amazing species, the more motivated we'll be to protect them. Learn more about how you can help by visiting the Australian Platypus Conservancy.

View Article Sources
  1. Leary, C. "IUCN Red List Of Threatened Species: Zaglossus Bruijnii". IUCN Red List Of Threatened Species.

  2. "Zaglossus Bartoni (Eastern Long-Beaked Echidna)". Animal Diversity Web.

  3. Leary, C. "IUCN Red List Of Threatened Species: Zaglossus Bartoni". IUCN Red List Of Threatened Species.

  4. Leary, C. "IUCN Red List Of Threatened Species: Zaglossus Attenboroughi". IUCN Red List Of Threatened Species.