[Illustration: _Fig. 157. Rose infested with aphids or plant-lice._] Very soon after the green leaves come, one may notice that the ants seem to be greatly interested in getting to the tops of trees, bushes and vines. If one watches for only a short time, he may see them hastening up and down with that important ant-air which says plainly, "There now, don't hinder me, I haven't a moment to waste." If we should follow with our eyes one of these hurried six-footed Marthas on her way up a tree, we would find that her business was that of milk-maid. Her cows are there pasturing on the leaves overhead, and she hastens to them coaxing for the milk, which is a clear drop of sweet honeydew. For many years entomologists repeated the statement that the honeydew secreted by aphids or plant-lice for the use of the ants came from the two little tubes on the back of the insect. It is easy to see how this mistake came about; the tubes were there, and so was the honeydew; the tubes suggested a cow's udder, and as the ants use the honeydew the natural inference was that it came from the tubes. This interesting error has been printed in so many honorable books, that it has become a classic. As a matter of fact, the caterpillars of our little, blue butterflies do have glands on the abdomen which secrete honeydew for the use of the ants; but the honeydew of the plant-lice, like honey itself, is manufactured in the alimentary canal, and issues from it. Observations have shown that each individual plant-louse may produce from five to seven drops of honeydew in twenty-four hours. If our cows could produce as much in proportion, then a good Holstein would give something like six thousand pounds of milk per day, and would be a highly profitable animal to have in the dairy. Although the honeydew does not come from the little tubes on the back of the plant-louse, yet those tubes have their uses. I once observed a young spider approaching an aphid, which was facing its enemy. As the spider approached, the aphid lifted its abdomen, and thrust one of these tubes over directly in the spider's face, and on this tube there suddenly appeared a little ball of yellow wax. The whole act was so like a pugilist thrusting his fist in his enemy's face that I laughed. The spider retreated and the aphid let its abdomen fall back in its natural position, but the little wax ball remained for some time on the tip of the tube. A German scientist, Mr. Busgen, of the University of Jena, discovered that a plant-louse smeared the eyes and jaws of his enemy, the aphis-lion, with this wax which dried as soon as applied. In action it was something like throwing a basin of paste at the head of an attacking party. Mr. Busgen discovered that the aphis-lion thus treated was obliged to stop and clean himself before he could go on with his hunt, and meantime the aphid walked off in safety. [Illustration: _Fig. 158. A stable made by ants for plant-lice._]