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Echidna also called spiny anteater, either of two species of egg-laying mammals constituting the family Tachyglossidae, order Monotremata. These stocky, virtually tailless, brownish-furred animals have strong-clawed feet and, on the upper part of the body, spines as well as hair. The spines vary in colour from white and yellow to black. Echidnas of the genus Zaglossus, the several forms of which are usually considered races of Z. bruijni of New Guinea, are 45 to 78 cm (18 to 31 inches) long and rather piglike, with short, wide-set spines. The other species, Tachyglossus aculeatus, found in many habitats across Australia and Tasmania (the latter population sometimes considered a separate species, T. setosus), is 35 to 53 cm (14 to 21 inches) long and has spines like a hedgehog's. Z. bruijni, which is valued for its meat, is declining in numbers as a combined result of forest clearance and unrestricted hunting.
To frustrate enemies, an echidna may roll into a ball and dig straight down in loose soil, or it may wedge itself tightly into a crack. Males have spurs on the hindlegs, presumably for combat. Both genera have a narrow, sensitive snout (longer and decurved in Zaglossus), a small mouth, and an extensible sticky tongue for feeding on termites and ants. An echidna can fast for a month.
The female lays a single egg, which is transferred into a pouch she developed in the breeding season. Incubation takes about 10 days. The young receives milk, exuded from the nippleless mammary openings, for about seven weeks; then the mother hides its young in a nest of leaves. An echidna may live from 30 to 50 years in captivity.
Superficially, the echidnas are quite unlike the platypus. They have a rounded body covered on the back and sides with stout, sharp-pointed spines and some hairs. The spines of Tachyglossus may measure up to six centimetres (2.5 inches) in length, those of Zaglossus up to about three centimetres. The undersurface is covered with coarse hair and is usually without spines. The colour of the spines and hair ranges from light brown to almost black, depending on species and individual variation. Adult males are larger than adult females. There is a long, naked, and sensitive muzzle, a very short tail, and no neck. In some echidnas a definite external ear is present, but in others it is inconspicuous. The nostrils open near the tip of the muzzle. The mouth is small, only sufficient for the protrusion of the long, sticky tongue. The limbs are short and powerful and have strong claws for digging. In Tachyglossus one of the claws of the hind foot is particularly elongated and is used for scratching the skin between the spines.
The echidnas resemble the platypus in that there is a venom apparatus on each hind leg, but the spur and crural gland are smaller. In Tachyglossus, the spur (about five to 10 millimetres [0.2-0.4 inch] long), which is situated on the inside of the ankle, is present in all males and some females. No observations on the use of the venom apparatus by the echidnas have been published.
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