The members of this family are well known in most parts of the world in the larval state as “bots,” internal parasites in the stomach of the horse, in the nostrils of sheep, and the skins of cattle. The life history of the common European bot-fly, _Gastrophilus equi_, is well known; the active fly lays her eggs upon the shoulders or jaws of the horse, attaching them to the hair by a gummy secretion; the horse licking itself transfers the eggs into its mouth, where the tiny maggots hatch out and are carried down into the stomach. They are provided with a pair of fine curved hooks in front of the head by which these little creatures hook themselves into the membrane of the stomach, absorbing their nutriment from the liquid with which they are surrounded. When fully developed these oval spiny bots detach themselves and pass out with the excrement, the maggots at once burying themselves in the damp soil and pupating; the perfect fly emerges early in February in most parts of N.S. Wales. The flies, about ½ an inch in length, have large thickset bodies thickly clothed with short brown or golden hairs, giving them the general appearance of a hairy bee; the male has a short rounded abdomen; that of the female is greatly elongated and usually curled up underneath. There are probably several introduced species now common in Australia with a wide range over the country. It is remarkable that though they do not bite or sting the horses when laying their eggs, yet as soon as the horses hear the loud hum of the bot-fly they gallop about and show an inherited fear of this pest, which, though it does not kill them, must be a very unpleasant parasite when numerous. The members of the Genus _Hypoderma_ are a very serious pest in Europe and other countries where they infest cattle, and are known both as “warble” or “bot-flies.” The fly lays her eggs upon the back of the beast; the tiny larva makes its way through the hide, beneath which it lives and feeds upon the putrid matter caused by the irritation of its presence; it finally produces an inflamed blister-like swelling or “warble,” eventually working its way out through the hide and falling to the ground, where it buries itself and pupates. No species have been found in Australia, but in some parts of England very serious damage is caused to the health of the beast, and the skin by being perforated loses value for making leather. [Illustration: =Fig. 151.=--_Gastrophilus equi_ (Fabr.). 1 and 2, The introduced Bot-fly, showing dorsal and lateral view of female; 3, eggs attached to hairs of horse; 4, egg enlarged (the eggs should be more truncate at the tips); 5, larval bots attached to piece of the stomach of a horse; 6, bot much enlarged; 7, enlarged head of bot showing the mouth hooks.]