Whole tracts of land are devastated by these winged armies. In the south of England some of you have seen, during the last dry summer that we had, what legions of caterpillars covered vast tracts of land, eating every vestige of green and leaving bare stalks where fine cabbages and other crops had been looked for. Ravagers of forests, also, some of these insignificant insects have been called, and with good reason. The term locust we take as a symbol, and we will include here the various groups of tiny beings which, by reason of their vast numbers and the way in which they come and go “in bands,” become such formidable enemies of our race. The caterpillars of the large white cabbage butterfly, and also those of the small white species, attack several valuable crops besides cabbages. They consume in the larvæ stage an enormous amount when their size is considered. Mr. Wood tells us that it has been calculated that one caterpillar alone, a month after birth, has increased to ten thousand times its original weight on leaving the egg, and has devoured in the meantime no less than forty thousand times that weight in food; and although during the winter months it may be frozen into a brittle condition, it survives this frost uninjured and becomes itself the parent of two broods during the ensuing summer. These particular caterpillars feed also on the leaves of turnip plants and on the pods that are left for seeding; they eat radishes, horse-radish and water-cress. [Illustration] Some years they show in myriads. Describing a flight of butterflies that arrived on a certain day years ago, the _Zoologist_ says that it was one of the largest flights ever seen in this country. It crossed the Channel from France on a Sunday in July. “Such was the density and extent of the cloud formed by the living mass that it completely obscured the sun from the people on board our Continental steamers. The decks were strewed with the insects in all directions. The flight reached England about twelve at noon, and dispersed themselves inland and alongshore, darkening the air as they went. During the sea-passage of the butterflies the weather was calm and sunny, with scarcely a puff of wind stirring; but an hour or so after they reached _terra firma_ it came on to blow great guns from the south-west, the direction whence the insects came.” On a calm sea the butterflies are able to settle frequently, as though the water were land, and to rise again; otherwise, that is, in windy weather, these long flights would be of course an impossibility. Louis Figuier, a French entomologist, has told how a swarm of plant lice once appeared between Bruges and Ghent, “hovering about, in troops” in such numbers as to darken the light of day. The walls of the houses were so covered that they could no longer be distinguished, and the whole road from the one town to the other was rendered black by the legions of this insect. These were called “smother-fly.”