The insect fauna of Australia is as remarkable and distinctive in its peculiarities as the flora, and probably for the same reason,--the fact of its isolated position from the larger continental areas, and the configuration of the continent. If we take away the eastern mountain range running north and south from Cape York to Gippsland, we find an immense tract of almost level country with hardly a river of any size except the Murray and its tributaries, covered with thick scrub or open forest, great flat unbroken plains in the south; rolling downs towards the north; sand-hills, and low timbered ranges in the interior. It is half the year without any permanent water for hundreds of miles at a stretch; scorched with a blazing sun and fierce hot winds in summer, bleak and cold in the winter. Yet there is no desert country of any extent in the strict sense of the word in the most arid portion; for given a good fall of rain, the country, apparently parched beyond recovery, soon puts on a coat of green, wild flowers shoot out, insects and little creatures of all kinds emerge from their hiding places, and birds appear as if by magic. Naturally our fauna, and the insects in particular, have had to adapt themselves to these extremes, and we find them with many curious habits without parallel in more normal countries. Our fauna is extremely rich in gall-producing insects in many different orders; there are about 50 different species of coccids that form well defined galls upon their host plants, yet the only record of a gall-making coccid outside Australia is a single species in Mexico. Numbers of _Thripidae_ produce galls in the leaves or flower buds of our native shrubs, while the galls of _Psyllidae_, _Diptera_, and _Hymenoptera_ are very abundant. Ants, _Formicidae_, swarm in the driest parts of the interior; and flies, of all kinds, blow flies, blue bottle, and the small house flies, are a perfect pest all through the summer months. All our coastal scrubs are rich in flowering shrubs which provide food or hunting ground for a large insect population. The flower wasps, _Thynnidae_, (in which the males are large and handsome with well developed wings, but the females are diminutive and wingless,) comprise several hundred described species; the only other countries in which they are represented are the west coast of South America, and a few in the Pacific Islands. The allied ant-like _Mutillidae_ with their wingless females are more numerous in the interior. Though our country is very rich in Sawflies, _Tenthredinidae_, they all belong to genera peculiar to Australia; the members of the typical genus _Cimbex_ extending its range as far east as Japan do not reach us.