obey. Population growth, positive or negative, up or down, is of life-and-death importance to any ant colony. Constant population growth and ever-rising productivity in the nurseries are the superorganism's bottom line. Both social and personal life are geared to serve this central purpose. The reason is elementary: the larger the colony, the greater its net growth, and hence the more virgin queens and males it can contribute to the next generation of colonies. Genes that prescribe robust colony growth spread across the land and through the species as a whole; those that do not prescribe robust growth shrink before the expanding Darwinian winners, and disappear.
The Trailheader myrmidons themselves instinctively knew they were in trouble. In time the chemical signals had dropped to a hardly detectable level in the outermost reaches of the nest. The workers began to understand that their Queen was incompetent.
Still, the instinct machine could not be turned off. The pheromone messages continued. They flowed ant to ant, spreading the latest news, the gossip, the health and wealth of the commonweal. The worker castes performed as before, and foragers still left in the early morning to search for food in the surrounding terrain. But the Trailheader workers had begun to change in subtle ways. The throttle of the colony was easing, a little at a time.
The Queen's health had been declining weeks before her death. The clues were all around her. Her egg production had plummeted, then halted. There were fewer and fewer larvae to feed. More nurse workers were idled, and colony growth slowed. The number of foragers taking the field dropped.
Yet there was hope for the colony. Even when the Queen still lived, the thinning of her pheromones had caused subtle changes in the bodies of young soldiers headquartered in the nest. These largest members of the worker caste had massive heads filled with powerful muscles, which slammed their sharp-toothed jaws together like serrated wire cutters. They were the iron, the physical power, the instinctual viciousness of the colony. They usually served only to defend the nest from intruders. Sometimes they went out along the odor trails with the ordinary workers to guard large food sources against rival colonies. But they also had the ability to reproduce. Their capacious abdomens contained a half dozen ovaries that, when enlarged by further growth, could produce viable eggs. Amazons all, they could change from warriors to mothers.
As the Queen pheromone declined, the soldiers were alerted. The sensory cells in the outer segments of their antennae noted the change. The information was relayed along nerve cells to the soldiers' brains. Circuits within the brains transmitted instructions to endocrine glands located elsewhere in the head. The hormones released from these glands stimulated growth in the ovaries of the young soldiers. Lines of eggs then appeared inside the ovaries. They began as microscopically small masses near the outer tips of the ovaries. The eggs grew in size as they migrated downward toward the openings of the ovaries, reaching maximum size just before they were laid.
The soldiers with the potential to become the new queens of the Trailhead Colony and no longer inhibited by the mother Queen pheromone abandoned their regular duties. With their ovaries swelling with eggs, they moved deeper into the nest interior and closer to the dwindling piles of larvae and pupae. As the last shards of the old Queen's body were carried into the cemetery, several of her rival successors began to lay eggs. They were now soldier-queens, and the only hope the colony had to restart its own growth.
The ordinary workers around them accepted the new status of the soldier-queens. Their tolerance represented a profound shift in the behavior of the colony as a whole. If the mother Queen had remained alive and well, and she had continued to broadcast her special scent, the response to any usurper would have been swift and violent. The Trailhead Colony had previously obeyed a basic rule of antdom: to reproduce in the presence of a healthy queen is strictly forbidden. The odds against success of such an affront to authority are long. The gamble is dangerous, and only a very few make the attempt. When a usurper starts to lay her own eggs and place them among those of a healthy queen, or even when she just becomes capable of doing so, she is harassed by her nestmates. Her sisters refuse to regurgitate food to her. They climb and stand over her, pulling at her legs and antennae. They may use