The Sheep Nostril Fly, _Oestrus ovis_, has a wide range over the world, and was probably introduced into Australia many years ago, though it has been noticed only quite recently as a serious pest. This fly lays living maggots in the nostril of the unfortunate sheep; the maggots work their way up into the frontal sinuses of the head, where they remain until fully developed, when they turn downward and are usually sneezed out by the sheep in their efforts to get rid of the obstruction. The fly is slightly under ½ an inch in length; the upper surface of the head and body are grey to dull yellow, spotted or mottled with darker tints; the abdomen is yellowish mottled with darker markings. It has been found chiefly in the Blue Mountains N.S.W. Family 23. Louse or Spider Flies. HIPPOBOSCIDAE. These are parasitic Diptera, that having taken to idle and slothful habits (though some of them can fly very well), take up their quarters among the fur or feathers of different animals and birds, where they live and are carried about by their hosts. To suit this method of existence they have become quite altered in structure; they have flat leathery bodies, and their feet are produced into large pincer-like claws which enable them to cling to the skin of their host. Some have large wings with stout nervures but very rudimentary venation; a few though provided with wings at birth bite them off soon after; and others like the well known “sheep tick” are wingless. As a rule their presence even when numerous does not seem to incommode the infested animals after they have become used to them, for the wild ponies in the New Forest in England are often covered with the horse-fly, _Hippobosca equi_, and they take no notice of them. Yet if one alights upon a horse unaccustomed to the presence of the fly he becomes almost crazy with fright, probably from the pinching or tickling sensation produced by their claws. [Illustration: =Fig. 152.=--_Ortholfersia macleayi_ (Leach). A parasitic fly that lives upon wallabies. Figured by me as _Olfersia macleayi_ (Leach) in the “Agricultural Gazette,” N.S.W.] The Common European Sheep Tick, _Melophagus ovinus_, was introduced at a very early date into this country among the wool on the backs of sheep. It is a dark-brown, wingless creature thickly clothed with fine hairs, more like a stout-legged spider than a fly in general appearance, but it has not the requisite fourth pair of legs. These bristly legs are furnished with the usual stout curved claws, between which is a slender appendage like a short string, supposed to be used to hang on with by coiling it round the wool. From their blood-sucking habits and these pincer-like claws, they are very annoying to the sheep when numerous.