This species is found in France, in Italy, and also in the East, especially in Persia, and rarely in England. During the months of July and August the _OEstrus_ frequents pastures, and deposits its eggs chiefly on the shoulders and knees of horses (PLATE I.). In order to do this, the female suspends herself in the air for some seconds over the place she has chosen, falls upon it, and with her abdomen bent, sticks her eggs to the horse's hairs by means of a glutinous liquid with which they are provided, and which soon dries. This is repeated at very short intervals. It often happens that from four to five hundred eggs are thus deposited upon the same horse. Guided by a marvellous instinct, the female _OEstrus_ generally places her eggs on those parts of the horse's body which can be most easily touched with the tongue, that is, at the inner part of the knees, on the shoulders, and rarely on the outer part of the mane. [Illustration: Fig. 43.--Eggs of the Gad-fly (_OEstrus_ [_gasterophilus_] _equi_) deposited on the hairs of a horse.] The eggs of the _OEstrus_, which are white and of conical form, adhere to the horse's hair, as shown in Fig. 43. They are furnished with a lid, which at the time of hatching opens, to allow the exit of the young larva, which takes place, according to M. Joly, about twenty days after they are deposited. In fact, it is not in the egg state, but really in that of the larva, that the horse, as we shall explain, takes into his stomach these parasitical guests, to which Nature has allotted so singular an abode. When licking itself, the horse carries them into its mouth, and afterwards swallows them with his food, by which means they enter the stomach. It is a remarkable fact that it is sometimes other insects, as the _Tabania_ for instance, that by their repeated stinging cause the horse to lick himself, and thus to receive his most cruel enemy. In the perilous journey they have to perform from the skin of the horse to his stomach, many of the larvæ of the _OEstrus_, as may be supposed, are destroyed, ground by the teeth of the animal, or crushed by the alimentary substances. There is hardly one _OEstrus_ in fifty that arrives safely in the stomach of the horse; and yet if one were to open a horse which had been attacked by the _OEstri_, the stomach would be nearly always found to have many of the larvæ sticking to its inside. Fig. 44, taken from a drawing which accompanies M. Joly's Memoirs, represents the state of a horse's stomach attacked by the Gad-fly larvæ. [Illustration: Fig. 44.--Portion of the stomach of the horse, and larvæ of OEstrus (gasterophilus) equi.]