"However, besides this rapid increase of the corn-root aphids, there is something else that helps them to be so formidable a pest. And this is that they find very good and zealous friends in the millions of little brown ants that also live in the Illinois corn-fields. These swift, strong, brave little ants make their runways and nests all through the corn-fields, and are very devoted helpers of the soft-bodied helpless aphids. For the aphids pay for this help by acting as 'cattle' for the ants. "This is what Professor Forbes, a very careful and a very honest naturalist, found out about the ants and the aphids. The eggs of the aphids, hosts of shining black, round, little seed-like eggs, are laid late in the autumn. These eggs are gathered by the ants and heaped up in piles in the galleries of their nests, or sometimes in special chambers made by widening the runways here and there. All through the winter these eggs are cared for by the ants, being carried down into the deeper and warmer chambers in the coldest weather, and brought up nearer the surface when it is warm. When the sunny days of spring begin to come, the eggs are even brought up above ground and scattered about in the sunshine, then carried down again at night. The little ants may be seen sometimes turning the eggs over and over and carefully licking them as if to clean them of dust-particles. "In the late spring the aphid eggs hatch, and the young must have sap to drink right away. Their little beaks are thirsty for the plant-juices that are their only food. But there are no tender corn-roots ready for them in the fields because the corn has not yet been planted. What, then, shall the hungering baby aphids and their foster-mothers, the little brown ants, do? "This is what happens. Although it is too early yet for the corn to be growing, there are various kinds of weeds that begin to sprout with the coming on of spring, and two of these, especially, the smart-weed and the pigeon-grass, abundant and wide-spread in all the Mississippi Valley, are sure to be growing in the fields. While the aphids much prefer corn-roots to live on, they will get along very well on the roots of smart-weed or pigeon-grass. So the clever little brown ants put the almost helpless baby aphids on the tender roots of these weeds, and there their tiny beaks begin to be satisfied. Don't you call that clever, Mary?" "Clever! Gracious!" says Mary. "Do you know Professor Forbes? Is he really--does he always tell the--" I interrupt. I am sensitive about such questions. I answer rather sharply. "Yes, I _do_ know him; and yes, he always tells the truth. Don't interrupt any more, please, for there is still more of the story." Mary is silent.