They have spines like hedgehogs and they are sometimes called spiny anteaters because they feed on ants, termites, earthworms and other burrowing prey with their long, tube-like tiny mouths, toothless jaws and sticky tongue.
Their spines are golden brown to black for the most part, although a few albino echidnas have been found with pink eyes and white spines. These solitary mammals have mammary glands — and lay eggs.
To help them search for their prey in the soil, Echidnas are equipped with electroreceptors in their beaks which is similar to platypuses and this is not a coincidence.
Even though echidnas are land animals, they evolved from amphibious ancestors similar to platypuses. They now have strong limbs and claws for digging and just by looking at them, it would be hard to figure out that their ancestors were not fully land animals.
There is even more to it because mammals evolved from fish that have swim bladders homologous with lungs. They evolved these swim bladders because the ancestors of all fish, except cartilaginous fish, lived either in a shallow aquatic environment, periodically drying lake or swampy water, poor in oxygen.
Echidnas made another full circle by evolving adaptations to land habitat and abandoned the aquatic habitat again.
Echidnas and platypus are the only egg-laying mammals, known as monotremes. These spiky cuties live about 15-16 years in the wild but have been reported to live as long as 50 years under the right conditions. If you see one in the wild, you can determine the sex by size (of the adults) with males being 25% larger than the females on average. Fully grown a female can weigh up to 4.5 kilograms (9.9 lbs) and a male can weigh up to 6 kilograms (13.2 lbs).