The insect appears discouraged. In vain I replace the caterpillar by one of my reserve of Grey Worms: the Ammophila scorns the substituted prey. Besides, evening is drawing in, the sky has clouded, there are even a few drops of rain falling. In these circumstances it is needless to look for a renewal of the chase. Everything, therefore, ends, without my being able to use my Grey Worms as I had proposed. This observation kept me engaged, without a moment’s respite, from one o’clock in the afternoon until six o’clock in the evening. CHAPTER XIX AN UNKNOWN SENSE I have described the Ammophila’s hunting tactics in detail. The facts which I ascertained seem to me so rich in results that, even if the harmas laboratory supplied me with nothing more, I should think myself indemnified by this one observation. The surgical methods adopted by the Wasp with the object of paralysing the Grey Worm are the highest manifestation in the realm of instinct that I have hitherto met. This inborn science is eminently calculated to give us food for thought. What a subtle logician, what an unerring operator is that unconscious physiologist, the Ammophila! He who would witness these marvels for himself can hardly count on what a country walk may happen to show him; besides, if the lucky opportunity did present itself, he would not have time to profit by it. An observation, which I kept up for five hours on end, without even then managing to complete the experiment and obtain the proofs which I anticipated, is one that, to be properly conducted, should be made at leisure in one’s own garden. I owe my success, therefore, to my rustic laboratory. I make a present of the secret to whosoever would continue those magnificent studies: the harvest is inexhaustible; there will be sheaves for all. When we follow the Ammophila’s hunting in the due sequence of her actions, the first question that suggests itself is this: how does the Wasp go to work to recognize the spot beneath which the Grey Worm lies? There is nothing outside, nothing, at least, perceptible to the eye, to indicate the caterpillar’s hiding-place. The soil that conceals the quarry may be grassy or bare, flinty or earthy, smooth or seamed with little cracks. These varieties of appearance are matters of indifference to the huntress, who prospects every spot without showing preference for one more than another. At no place where the Wasp stops and digs with some persistency do I see anything particular, in spite of all my attention; and yet there must be a Grey Worm there, as I have but now convinced myself, five times in succession, by lending a helping hand to the insect, which was at first discouraged by a task out of proportion to its strength. Sight, therefore, is certainly out of the question here.