Swimming along the bottom of a freshwater stream or lake, a platypus probes among the mud and gravel with the highly sensitive end of its rubbery bill. Until recently, it was thought that edible material is located by the sense of touch alone, since the eyes and ears are closed when submerged, and that only those foodstuffs touched with the bill are snatched from the bottom. However, experiments by Scheich et al. When sufficient prey has been gathered and stored in the cheek pouches, or when breathing becomes necessary, the platypus proceeds to the surface and planes out with limbs outstretched and flattened tail trailing behind. Mastication of the food is accomplished by crushing and grinding it between the horny plates that act as teeth.
Grit taken up with foodstuffs probably serves as an abrasive to aid in mastication.
The diet consists of crayfish, shrimp, larvae of water insects, snails, tadpoles, worms, and small fish. In captivity, the platypus has been known to eat food equivalent to about half its own weight in a day. The platypus mates from August to October. Mating takes place in the water and is preceded by an unusual and intricate courtship during which, among other maneuvers, the male grasps the female's tail and the two animals then swim slowly in circles. The female carries bundles of wet leaves under her forwardly folded tail into the nest chamber.