The original natural cover of the New Zealand land mass before the human era was forest, tussock grasses, and sparsely covered or bare mountain lands. Through the replacement of vast areas of the forests by introduced grasses, many endemic species of insects, mites, and spiders are probably extinct. Insects abound in all habitats from the shore line to the high mountain regions. There are several associated with salt water, such as the salt-water breeding mosquito, the marine caddis fly, and marine mites. In the littoral zone, New Zealand has a rich community of insects and other organisms which live on decaying seaweed and seashore debris. Kelp flies are important New Zealand members of this community. Salt-water marsh lands have a distinctive and peculiar fauna including some species which tend to a subapterous condition. The forested areas provide a multitude of different ecological habitats. The North Island rain forest associations differ from the southern beech forests and some insect orders show distinct segregation of species in the two areas. Native tussock grasses still occur over extensive areas but the insect fauna of these areas has not been seriously studied. Some insects are found in the alpine areas, and such organisms as mites, springtails, harvestmen, and micro insects abound in forest litter. Intensive studies have been made on some of these insects and the conclusions drawn from such studies have been used in formulating theories on the past geography of New Zealand. Fresh-water lakes and rivers have an abundant fauna of bugs, beetles, flies, and caddis flies. Off-shore islands in many instances still retain much of their original vegetation and are important as localities of species which have become extinct on the mainland. Sub-Antarctic islands vary from the barren rocks of Bounty Islands to the tussock and low stunted forest of Auckland Islands. The insect fauna of these islands is sparse and is a peripheral one of the New Zealand subregion.