Hatchlings are about 1.5 cm long and weigh between 0.3 and 0.4 grams. After hatching, young Echidnas are known as "puggles". Hatchlings attach themselves to their mothers' milk areolae, a specialised patch on the skin that secretes milk (monotremes have no nipples). The way in which puggles drink the milk is not yet known, but they have been observed drinking large amounts during each feeding period, since mothers may leave them unattended in the burrow for between five and ten days. The principal components of the milk are types of lactose. The milk has a high iron content, which gives it a pink colour.