These latter, by merely touching an insect with their antennæ, can tell if it is already occupied—in which case they withdraw—nor do they ever lay eggs in excess of the number of issuing larvæ that can be supported by the little world of provender into which they will be born. Neither do they choose a caterpillar to lay on, which is just about to cast its skin, by which manœuvre the host would escape, and the guests be left to perish. All these mistakes, however, are frequently made by the Tachina fly, the consequence being that many poor children die of starvation; whilst others, from wanting their necessary complement of food, have their growth checked and become poor pitiable objects, less than half the size that, with a more generous diet, they would certainly have attained to. It is painful to know that such privation exists and to have no means of relieving it; but nature is full of sadness, and it is best to look truth in the face. Some comfort may perhaps be derived by looking forward to a distant future, when the instinct which is now liable to these errors shall have been perfected. Such comfort, at any rate, lives in Mr. Leland Howard’s views that “the parasitic mode of life in the Tachina fly is one of comparatively recent acquirement, and that sufficient time has not elapsed since they began to take on this habit”[17] to allow of its having reached the final goal towards which it is always advancing. It is difficult, however, to console oneself for the imperfections of a work-a-day world in a far distant prospect of Elysium. In the somewhat numerous list of insects distinguished by the attentions of the Tachina fly, grasshoppers have been mentioned. In Africa they, or, at any rate, one species of the family, attack the terrible plague locust, that has from time to time committed, and still apparently commits, such terrible devastations. The latter seems quite aware of the fate in store for it, and makes vigorous efforts to evade its destiny. Buzzing in the air, above the ravenous horde, the fly waits for one to hop or rise on the wing, and then darts swiftly upon it. To avoid her, the locust rises or sinks, tacks suddenly to right or left, scudding this way and that like a ship to meet a varying breeze. The Tachina, in the meanwhile, circles about her quarry, awaiting a favourable opportunity, which generally arises just as the locust alights, or is on the point of alighting, when, descending upon it before the lost impetus can be renewed, she clings lovingly, and deposits her eggs, either on the neck or under one of the wings, “——and with a little pin Bores through his castle wall, and farewell king.”