Planet of the Bugs: Evolution and the Rise of Insects Read Free

only recently developed over the last several thousand years. Insects have successfully coevolved with terrestrial ecosystems over the last four hundred million years. They are ecologically essential as scavengers, nutrient recyclers, and soil producers, feeding on and utilizing virtually every kind of imaginable organic material. Six-legged detritivores consume dead plants, dead animals, and animal droppings, greatly increasing the rates at which these materials biodegrade. Insects, as both predators and parasitoids, are keystone organisms that feed upon and reduce populations of other kinds of plant-feeding and scavenging insects. They are also their own worst enemies: most kinds of insects have populations that are kept in check by the feeding activities of other insects.
    Over the past 120 million years, insects have coevolved and explosively diversified in tandem with the angiosperms—the dominant forms of plant diversity in modern ecosystems. They are essential as pollinators and seed-dispersers for most of the flowering plants, whose communities would be vastly diminished if all plant-associated insects were eliminated. We often tend to think of plant-feeding insects in general as pests, but I like to point out that only a miniscule small fraction (less than 1 percent) of the total number of insect species are actually significant pests. In fact, most of the plant-feeding insects should be considered beneficial for two reasons. First, they reduce the reproductive output of particular plants by putting stress on them. That sounds bad if the plant is an agricultural crop, but in a natural setting, such as a tropical forest or a mountain meadow, that plant feeding has a very desirable outcome. It prevents particular plant species from becoming superabundant and weedy, allowing vastly more species to coexist in much smaller spaces. Plant-feeding insects are a driving force in the evolution of plant community species richness, and so the extraordinary plant diversity of tropical habitats islargely due to insect diversity, not despite it. Second, but of no less importance, the majority of plant-feeding insects are themselves edible to other kinds of wildlife. Many insects are a fundamental and nutritious food source for most kinds of vertebrate species, including fish, amphibians, reptiles, birds, and most mammals, including primates and even humans. Not many organisms totally depend on humans for their continued existence, but a large part of living plants and terrestrial animals depend partly or entirely on insects for their survival.
    Whether or not they rule the planet, insects certainly have largely overrun it. They can be found in abundance in virtually every kind of terrestrial habitat, from tropical rain forests to deserts, in meadows and prairies, from sea shorelines to alpine tundra and Andean páramo. Aquatic insects not only inhabit mountain streams, rivers, waterfalls, seepages, lakes, ponds, swamps, and salt marshes, but they even occupy mud puddles, sewage ponds, craters in rocks, tree holes, pitcher plant leaves, and bromeliad leaf bases more than a hundred feet above the forest floor. Semiaquatic insects exploit the force of surface tension to skate across still ponds and lakes, while the ocean water strider, genus
Halobates
, has been seen walking on the ocean surface hundreds of miles at sea. Clouds of millions of African migratory locusts have flown across the entire Atlantic Ocean to land in the Caribbean Islands. The insect macro-societies, ants and termites, are essential soil movers in the Amazon basin, where their biomass outweighs the biomass of vertebrates. But sheer insect abundance is not strictly a tropical phenomenon. Even near the Arctic Circle, the combined weight of biting flies and midges outweighs that of the mammals.
    Insects and their relatives have evolved and adapted to some of the most extreme conditions on the planet. Stoneflies have been recorded at an elevation of 5,600 meters in