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

concealed or protected environment. In contrast, adult insects with complete metamorphosis can concentrate their activities on courtship, mating, and egg production. Many feed on completely different resources from their young, or do not feed at all. The fact that more than 75 percent of all modern insect species have complete metamorphosis attests to the usefulness and success of this behavior.
    An inquiring student of insects might seek more sophisticated answers in the study of insect evolution over the past four hundred million years. An advanced course on this topic might cover the history of insects based on fossil remains, and relationships inferred by studies of anatomy, behavior, genetics, and molecular sequences. One would probably learn that the most ancient insects evolved on land in association with the most ancient land plants, in the Late Silurian or Early Devonian periods. By the Carboniferous period, the time of the great coal-forming swamps, insects had evolved wings. The innovation of flight allowed the first great radiation of insect species, including giant dragonfly-like insects and many other ancient species that no longer exist. By the Permian, insects were diversifying into increasingly modern forms, including species we would recognize as bugs, lacewings, and beetles. The development of complete metamorphosis in the Permian was a key innovation, perhaps, that allowed many insects to thrive and diversify in an unstable and changing world. Other insects, and many other creatures, were not so lucky.
    At the end of the Permian, our world experienced a massive extinction episode. In the oceans many ancient life forms, including the trilobites, disappeared for all time. On land several kinds of life went extinct as well, including some of the ancient insects that had flourished for millions of years. But others survived and diversified, especially those with complex metamorphosis. And so it was through the Mesozoic times, when the insects coexisted with the large dinosaurs. Sometime in the Early Cretaceous period flowering plants evolved, and insects adapted by rapidly evolving diverse new species. Along with the flowers came the insect associates: butterflies, bees, ants, and social wasps. Another major extinction event, perhaps triggered by a massive asteroid impact sixty-five million years ago, brought to a close the time of the big dinosaurs. The little feathered dinosaurs, which we now call birds, survived and flourished, as did many flowering plants and insect groups. And so it has gone through the Cenozoic: the ongoing coevolution of flowering plants and insects has generated awesome biological diversity and complexity in tropical forest ecosystems.
    The story of insect evolution, as revealed by their rich fossil history, though illuminating, is not completely satisfying. We might still wonder about the origins of the first insect. I began this chapter with a quote from Barry Hughart, who pointed out that “all events have an end and a beginning.” To gain a full understanding of something ascomplex as insect diversity on earth, we need to “understand correctly what comes first and what follows.” We need to delve even deeper into the insects’ prehistory, into the time before the Silurian myriapods heroically occupied the land, with their external skeletons and legs. The myriapods inherited these features from sea-dwelling Cambrian arthropods, which first developed body armor and mobility in response to increasing oxygen levels and predator activity in the oceans. So our story of insects must begin there in the earth’s ancient oceans, more than a half-billion years ago.

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    Rise of the Arthropods
     
About 600 million years ago . . . all hell broke loose in organic evolution.
DAVID RAUP,
Extinction: Bad Genes or Bad Luck?
     
Sometimes the destination isn’t as important as the drive.
CHRISTINA APPLEGATE,
Up All Night
     
    If you want to experience the geological ages of animal life