Animals Endangered Species What Are the 5 Mammals That Lay Eggs? By Amy Y. Conry Davis Writer University of San Diego Center for Documentary Studies at Duke University Amy Conry Davis works as a writer, content, creator, and photographer. She lives full-time in an Airstream and travels throughout the United States. our editorial process Amy Y. Conry Davis Updated April 01, 2021 Yvonne Van der Horst / Getty Images Share Twitter Pinterest Email Animals Wildlife Pets Animal Rights Endangered Species The following creatures all share a rather unique characteristic. They are mammals that lay eggs and also 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, western long-beaked echidna, eastern long-beaked echidna, short-beaked echidna, and Sir David's long-beaked echidna. All of these 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 set out to dig for ants, termites, and other small invertebrates using their highly adapted sense of smell. For the platypus, who is also nocturnal, rivers and waterways are their natural element. They can spend over 10 hours a night on the hunt for food which consists of small animals like shrimp and crayfish. What Are Monotremes? Monotremes are one group of mammals who reproduce by laying eggs. Their name comes from Greek and means "single opening." This refers to the distinguishing fact that they have only one opening for both reproductive and waste removal purposes. According to the IUCN's Red List, the Sir David's long-beaked echidna and the western long-beaked echidna are both critically endangered. The eastern long-beaked echidna is considered vulnerable. The platypus is near threatened and the short-beaked echidna has stable populations. 1 of 5 Duck-Billed Platypus Goddard_Photography / Getty Images This fascinating creature, with its distinct duck-like bill, 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 2 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. 2 of 5 Western Long-Beaked Echidna Posnov / Getty Images 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 the decline in its population. 3 of 5 Eastern Long-Beaked Echidna Posnov / Getty Images Like their western long-beaked relatives, these eastern echidnas are also much larger than the other monotremes. They are brown or black in color 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. 4 of 5 Short-Beaked Echidna Jarrod Callati / Getty Images 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 hedge hog. 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 during breeding season when searching for potential mates. 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. 5 of 5 Sir David's Long-Beaked Echidna Michael Barrett / EyeEm / Getty Images 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.