The fauna of flies is extensive and widespread throughout New Zealand and the off-shore islands, every type of habitat available in the New Zealand environment being occupied by some members of the order. A few of the 1,850 species so far known are of economic importance. These include houseflies, mosquitoes, and midges in the field of public health, blowflies and ked (sheep tick) in animal husbandry, leaf miners and root maggots in plant husbandry.
The more primitive sub-order (Nematocera) is well represented in the New Zealand fauna and most of the moist forests of the North Island and parts of the South Island have provided ideal ecological habitats for the evolution of numerous species. Thus New Zealand has a very strong crane fly fauna with at least 600 endemic species already described. Gnats are abundant and some species are present in very large populations. About 300 species are known, including the glow-worm. Mosquitoes and sandflies are exceedingly numerous in some moist bush localities and around some areas of the sea shore. In all, about 12 species of mosquitoes and eight species of simuliid sandflies are known. Midges likewise have huge populations of adults and of larvae (blood-worms) and New Zealand probably has more than 50 endemic species. There are many species of the biting midge family but only one species in New Zealand is known to bite. There are indications of a strong representation of the gall-midge family in New Zealand.
The more highly evolved flies of the sub-order Brachycera are with some exceptions not represented by large numbers of species in any family. The exceptions are the Dance flies and Dolichopodid flies. Both these families are represented by well over 100 endemic species. The large predacious flies are fairly common and some are the most striking and conspicuous members of the fly fauna. Among such flies are the horse flies, soldier flies, and robber or assassin flies. Most of them are beneficial in that they attack other insects. Hover flies are by no means uncommon and several species are important predators of aphids. There is a strong representation of species of small flies of size ranging from 2 to 4 mm. They belong to the acalypterate group of the sub-order. They are rarely noticed in the field but are of interest because they include the leaf-mining flies, the small fruit flies of the well-known genus Drosophila, the true fruit flies (which in New Zealand do not attack fruit but rather the seed heads of the Compositae), the shore flies of brackish water, and the kelp flies. The most highly evolved flies are the Muscids which in the widest sense include the houseflies, stable flies, biting flies, blowflies, and the many parasitic tachinid flies. A fauna of blood-sucking wingless parasitic flies is present on warm-blooded animals and on birds in New Zealand but no study has yet been made of them.
by Roy Alexander Harrison, D.SC., Senior Lecturer in Agricultural Zoology, Lincoln Agricultural College.