They had recoiled from the river instinctively. But their ancestors had never known fire. In the Amazon basin, on Earth, there had never been forest fires. On the forgotten planet there had never been fires at all, unless the first forgotten colonists tried to make them. In any case the army ants had no instinctive terror of flame. They marched into the blazing openings that appeared in the hills. They snapped with their mandibles at the leaping flames, and sprang to grapple with the burning coals. The blazing areas widened as the purple surface was consumed. Burl watched without comprehension--even without thankfulness. He stood breathing more and more easily until the glow from approaching flames reddened his skin and the acrid smoke made tears flow from his eyes. Then he retreated slowly, leaning on his club and often looking back. Night had fallen, but yet it was light to the army ants. They marched on, shrilling their defiance. They poured devotedly--and ferociously--into the inferno of flame. At last there were only small groups of stragglers from the great ant-army scurrying here and there over the ground their comrades had stripped of all life. The bodies of the main army made a vast malodor, burning in the furnace of the hills. There had been pain in that burning, agony such as no one would willing dwell upon. But it came of the insane courage of the ants, attacking the burning stuff with their horny jaws, rolling over and over with flaming lumps of charcoal clutched in their mandibles. Burl heard them shrilling their war-cry even as they died. Blinded, antennae singed off, legs shriveling, they yet went forward to attack their impossible enemy. Burl made his way slowly over the hills. Twice he saw small bodies of the vanished army. They had passed between the widening furnaces and furiously devoured all that moved as they forged ahead. Once Burl was spied, and a shrill cry sounded, but he moved on and only a single ant rushed after him. Burl brought down his club and a writhing body remained to be eaten by its comrades when they came upon it. And now the last faint traces of light had vanished in the west. There was no real brightness anywhere except the flames of the burning hills. The slow, slow nightly rain that dripped down all through the dark hours began. It made a pattering noise upon the unburnt part of the hills. Burl found firm ground beneath his feet. He listened keenly for sounds of danger. Something rustled heavily in a thicket of toadstools a hundred feet away. There were sounds of preening, and of feet delicately placed here and there upon the ground. Then a great body took to the air with the throbbing beat of mighty wings. A fierce down-current of air smote Burl, and he looked upward in time to glimpse the outline of a huge moth passing overhead. He turned to watch the line of its flight, and saw the fierce glow filling all the horizon. The hills burned brighter as the flames widened.