The structure and development of the marsupium, or pouch, of the female varies considerably between species. In kangaroos and koalas, for example, it is well developed. In some species, such as many of the small, terrestrial marsupial mice and the shrew opossums, the pouch is absent entirely. In other species, such as the mulgara of Australia, the pouch consists only of small folds of skin along the sides of the mammary area. Most marsupial pouches open toward the front, but those of the koalas and bandicoots open to the rear.
Males normally have no pouch.
Some marsupials are general carnivores, or meat eaters, and other species are general herbivores, or plant eaters. Still others prefer particular foods, and some are scavengers or omnivores that will eat almost anything. Perhaps the best-known example of a specialist is the koala, whose lifelong diet consists almost entirely of the leaves and bark of about a dozen species of eucalyptus trees. The numbat, or banded anteater, has a long tongue and lives on a diet of termites and occasionally ants. Many smaller marsupial species such as the marsupial mice and the shrew opossums are predators that eat insects and other invertebrates as well as small vertebrates.