PROLOGUE

      All animals must eat. If they don't, they cannot fulfill the three basic imperatives of life: to grow and to survive long enough to reproduce. But who eats whom, and why? Except for climatic factors such as droughts or freezing temperatures, predators are probably the most pervasive and dangerous threat to the survival of most animals. Because all organisms require food, the relationships between the eaten and the eaters are a—perhaps the—central aspect of what goes on in a community of organisms, which, together with their physical environment, constitute an ecosystem.

      In almost all land and freshwater ecosystems, insects are the most abundant animal food. Without a doubt, knowing the ways in which insects avoid becoming a meal for an insect-eating predator and the ways in which predators evade their defensive strategies is essential to understanding how ecosystems work. Moreover, these relationships are in themselves fascinating, sometimes bizarre, and always enlightening.

      Many, many different kinds of organisms make a living by preying on insects. They include a few plants, but most of them are representatives of virtually all the major animal groups (classes)—except those that live only or mainly in the seas: sponges, jellyfish, starfish, clams, and snails—ranging from spiders and insects to vertebrates such as lizards, birds, and mammals.

      Natural selection favors changes (mutations) that in one way or another improve an organism's ability to cope with its environment, to better exploit opportunities and avoid being eaten by a predator. “During evolution,” as J. R. Krebs and N. B. Davies wrote, “we expect natural selection to increase the efficiency with which predators detect and capture prey. On the other hand, we would also expect selection to improve the prey's ability to avoid detection and to escape. The complex adaptations and counter-adaptations we see between predators and their prey are testament to their long coexistence and reflect the result of an arms race over evolutionary time.”

      These adaptations and counteradaptations are multitudinous, diverse, and sometimes so extraordinary that they defy belief. A spider lures certain male moths to their deaths by counterfeiting the chemical sex attractant of females of the victims' species. A burrowing owl uses bait to attract the beetles that it eats. A praying mantis attracts its prey, nectar-seeking bees and flies, by masquerading as a large, colorful flower. Some ant lions and a few other insects dig pitfall traps and quietly wait, unseen, in the bottom to devour careless insects that stumble into the pit.

      A few caterpillars hoodwink insectivorous birds by posing as repulsive bird droppings. Certain nerve fibers of some fleet-footed insects are greatly enlarged to hasten the arrival at the central nervous system of nerve impulses, generated by the perception of a warning signal, that will trigger flight. Most moths are active only at night, and during the day many hide in plain sight,