He began cruising slowly, at random, across the rolling moonlit waste of wind-built dunes, watching for spoor. He spied, and swerved automatically to avoid, the cunningly concealed pit of a sand devil, strategically placed in a hollow of the ground. Cautiously Dworn circled back for a second look. The conical pit was partly fallen in, unrepaired; the devil was obviously gone. The burrowing machine would, Dworn knew, have had fuel and other supplies somewhere in its deep lair, buried beneath the drifted sand where it spent its life breathing through a tube to the surface and waiting for unwary passers-by to skid into its trap. But Dworn regretfully concluded that it would not be worth while digging on the chance that whatever had done away with the devil had not rifled its stores.... He swung the beetle's nose about and accelerated again. On the next rise, he paused to inspect the track of a pill-bug; but to his practiced eye it was quickly evident that the trail was too old, blowing sand had already blurred the mark of heels, and the bug probably was many miles away by now. A mile farther on, luck smiled on him at last. He crossed the fresh and well-marked trail of a caterpillar--deeply indented tread-marks, meandering across the dunes. * * * * * He began following the spoor, still slowly, so as not to lose it or to run upon its maker unawares. A caterpillar was a lumbering monster of which he had no fear, but it was much bigger than a beetle, and could be dangerous when cornered. Dworn had no wish to corner it; the caterpillar itself was not the object of his stalking, but one of its supply caches which according to caterpillar custom it would have hidden at various places within its range. The trail led him uphill, into a region cut by washes--dry now, since the rainy season was past--and by ridges that rose like naked vertebrae from the sea of sand that engulfed the valley floor. Several times Dworn saw places where the caterpillar had halted, backed and filled, shoved piles of earth and rocks together or scraped patches of ground clear with its great shovel. But the beetle knew his prey's habits of old, and he passed by these spots without a second glance, aware that this conspicuous activity was no more than a ruse to deceive predators like himself. If Dworn hadn't known that trick, and many others used by the various non-predatory machine species which manufactured food and fuel by photosynthesis, he would have been unfit to be a beetle--and he would never have lived through the wanderyear which weeded out the unfit according to the beetle people's stern immemorial custom.