Our final color experiment was to let the blue paper remain for a day or two, giving time for all the wasps to become familiar with it, and then to leave it on the ground a foot and a half away, while replacing it with yellow. This gave a false nest surrounded by the color that they had been associating with the entrance, and a true nest surrounded by a new color. In the next ten minutes two hundred and seventy wasps came home, and every one of them went to the false nest. Many circled above it, others entered the hole in the paper, and some began to excavate, and made quite a depression in the ground; but gradually they found their way home. Three hours later seventy–six wasps entered the false nest in five minutes, and at evening they were still visiting it in goodly numbers; but on the next day we saw only two that were deceived.
On successive days we substituted red for yellow, green for red, and so on, always with similar results, although the wasps became more and more accustomed to the vicissitudes of their life, and after a time seemed to look for the hole itself without relying upon the color to guide them. They found their nest under a color new to them much more readily than when the paper was taken entirely away and the ground left exposed. Once when the green paper was around their nest, and the wind blew it over the hole so that they could not enter, at least one hundred collected, many of them settling in the false nest; when we lifted the green paper, leaving the hole free, only three or four entered, but when we put it back in place they rushed in six or seven at a time. It was plainly the color that directed them.
This was a nearly rainless summer,—a condition extremely favorable to wasp development. Nests multiplied and grew until the whole country–side complained, and no wonder, for houses were full of them, and at mealtimes they gathered at the table with the members of the family. How did they know when dinner was ready? It could not have been by the sight, unfamiliar to them, of cooked food; was it, then, through the sense of smell?
Many were the questions that we asked in vain of our Vespas, but here was one that they could readily be made to answer. We rolled up two bundles, one of nothing but gauze, and another, like it in appearance, but containing some warm chicken bones; these were laid to one side of the nest, the color of the gauze matching that of the paper on which it was placed. The wasps in returning to the nest, even though loaded with food, could not resist the appetizing odor, and settled thickly upon the bone bundle, trying their best to penetrate within, while the empty gauze was unnoticed. As the bones grew cold and dry they attracted less attention, but two days later they were occasionally visited.