What are the only mammals that lay eggs?

In this brief article, we will provide an answer to the question, “What are the only mammals that lay eggs?”. We will also elaborate on the habitat, behaviour and reproduction of these mammals.

What are the only mammals that lay eggs?

Only two types of mammals lay eggs that include:

  • The duck-billed platypus
  • Echidna

The duck-billed platypus

The duck-billed platypus lives in water. The reproduction of platypus is different as compared to other mammals. Platypus is the only mammal to lay eggs other than echidna. 

Before hatching, the female platypus moves inside a burrowed chamber. The other distinguished features of the duck-billed platypus are a bill like ducks and a tail of a beaver.


Platypus prefers to live alone. During their lifetime, platypus either feed along the bottoms of rivers or dug burrows to live in them. Platypus is not sedentary rather they are full of energy. While hunting for larval insects and freshwater crustaceans, platypus move through streambed debris by using their flat bills.

The duck-billed platypus has a unique electromechanical system. They use this system to detect the presence of the prey by sensing their electrical signals. The entering point of the burrow of platypus is designed in such a way that only platypus can enter it. Extra moisture on the fur of platypus is removed by them.

Where does platypus live?

The duck-billed platypus is present only in Australia. They can be found in the Western flowing rivers in Queensland. The reason behind their presence only in Australia is because their ancestors took to the water. 

How does platypus reproduce?

Sperms are transferred in the female platypus through the cloaca. Cloaca is a solo opening by which urine, faeces and sperms pass.  In duck-billed platypus, the fertilisation of eggs takes place inside the body. The incubation and hatching of the eggs of a platypus take place externally.

The duck-billed platypus is polygamous. This means they are not restricted to only one mate. About two to four eggs are laid by females after 27 days of mating.

Benefits of platypus

Some benefits of the platypus are as follow

  • From the milk of platypus, we can extract antibiotics. These antibiotics are life-saving and are very beneficial. From these antibiotics, the treatment of diabetes can be carried out.
  • Several looming problems of humans could be treated by the milk of platypus.
  • Platypus also provides several ecological benefits. Like various insects, larvae, freshwater shrimps, and crayfish can be eaten by platypus. Otherwise, these insects can cause various problems for the soil.


Another name of echidna is spiny anteaters. Echidna is quill-covered that belongs to the Tachyglossidae family. The maximum lifetime of an echidna is forty years while the minimum lifetime is fifteen years. Feral dogs and foxes are the main enemies of echidna.

Echidna uses a waxy secretion during breeding. The production of this waxy secretion takes place around the base on the echidna spur. This waxy secretion is harmless. The distinguished feature of the echidna is the presence of spurs on the male’s hind legs.

Where does echidna live?

Talking about the habitat of echidna, these live in hollow logs under vegetation and piles of debris. Other than this, echidna also lives in open heathland, forests, shrublands and woodlands. When weather conditions become infeasible then echidnas protect themselves under bushes or by digging burrows in the ground.


Echidnas are monotremes. Monotremes don’t give birth to their off-springs but lay eggs. Male echidna can mate with females even when they are hibernated. Mating trains which are composed of eleven males and females are made by echidnas on Kangaroo Island. 

After forming matting trains, echidnas gather together and it is followed by intense bouts of courtship and sex for about two to six weeks.

The growth of eggs takes place inside the reproductive tract of the female echidna. Once it attains the size of a grape, it is laid. Each year echidna breeds once and the courtship takes about seven to thirty-seven days.

Benefits of echidna

Some benefits of echidna are as follow

  • Echidna is known as the engineer of the ecosystem. This is because echidnas play an essential role in enhancing the nutrients in the soil by digging it. Due to these nutrients, the growth of plants is enhanced and the diversity of species increases.
  • Echidna serves the role of bio-pesticides. These consume several insects and pests which are dangerous for the crops. Thus protects the soil from artificial pesticides which are also dangerous for the crops.


In this brief article, we have provided an answer to the question, “What are the only mammals that lay eggs?”. We have also elaborated on the habitat, behaviour and reproduction of these mammals.



Hi, I am Charlotte, I love cooking and in my previous life, I was a chef. I bring some of my experience to the recipes on this hub and answer your food questions.