Planet of the Bugs: Evolution and the Rise of Insects
Read Planet of the Bugs: Evolution and the Rise of Insects Online
Authors: Scott Richard Shaw
Scott Richard Shaw
is professor of entomology and Insect Museum curator at the University of Wyoming, Laramie.
The University of Chicago Press, Chicago 60637
The University of Chicago Press, Ltd., London
© 2014 by The University of Chicago
All rights reserved. Published 2014.
Printed in the United States of America
23 22 21 20 19 18 17 16 15 14 1 2 3 4 5
ISBN-13: 978-0-226-16361-1 (cloth)
ISBN-13: 978-0-226-16375-8 (e-book)
DOI: 10.7208/chicago/9780226163758.001.0001
Library of Congress Cataloging-in-Publication Data
Shaw, Scott R. (Scott Richard), author.
Planet of the bugs : evolution and the rise of insects / Scott Richard Shaw.
pages cm
Includes bibliographical references and index.
ISBN 978-0-226-16361-1 (cloth : alk. paper) — ISBN 978-0-226-16375-8 (e-book)
1. Insects—Evolution. I. Title.
QL468.7.S53 2014
595.7—dc23
2013050775
This paper meets the requirements of ANSI/NISO Z39.48–1992 (Permanence of Paper).
PLANET OF THE BUGS
EVOLUTION AND THE RISE OF INSECTS
Scott Richard Shaw
THE UNIVERSITY OF CHICAGO PRESS
CHICAGO AND LONDON
This book is dedicated to my wife, Marilyn, for her patience, support, and most especially understanding. Thanks for letting me keep bugs in the freezer. I couldn’t have done it without you
.
Contents
Prologue. Time Travel with Insects
The Cambrian period, 541–485 million years ago, and the Ordovician period, 485–444 million years ago
The Silurian period, 444–419 million years ago
The Devonian period, 419–359 million years ago
The Carboniferous period, 359–299 million years ago
The Permian period, 299–252 million years ago
The Triassic period, 252–201 million years ago
8. PICNICKING IN JURASSIC PARK
The Jurassic period, 201–145 million years ago
The Cretaceous period, 145–66 million years ago
The Cenozoic era, 66 million years ago to the present day
Postscript. The Buggy Universe Hypothesis
Color gallery follows Chapter 6
.
A long-horned beetle (family Cerambycidae) perches on a melastome leaf after a recent rain at San Ramon forest in Costa Rica.
Prologue: Time Travel with Insects
Time flies like an arrow. Fruit flies like bananas.
GROUCHO MARX
Late one October afternoon I was walking along a trail through the rain forest at San Ramon Biological Reserve in Costa Rica, pondering the nature of time and wishing for a time machine. The earth’s tropical wet forests do not display obvious seasonality so you would never guess the day, month, or year by looking at the surrounding mossy vegetation, and they emanate such an ancient and timeless green aura that it’s easy to imagine traveling back in time, thousands, hundreds of thousands, or even millions of years. The scent of decaying vegetation and fungus permeated the wet air, and the forest was both figuratively and literally crawling with insects. Around my feet, abundant small flies and other insects enjoyed the bounty of rotting fruits fallen to the forest floor. I recalled Groucho’s classic punch line in
Duck Soup
: “Fruit flies like bananas.”
As the songs of frogs, katydids, crickets, and cicadas emanated from the forest, my boots sloshed along the pathway. Typical of San Ramon, it had been raining all day, the trail oozed treacherously slick with slippery mud, and water was everywhere. On mushroom caps sprouting from a rotting log by the trail, silvery droplets rolled to the edge, clung briefly shimmering—then fell away. The sounds of water were all around, bubbling and gurgling over mossy rocks in the river, chattering in nameless streams and rivulets. A light mist was still falling, and the emerald vegetation, dappled in a hundred shades of green, was dripping and glistening with raindrops. The trees at San Ramon were matted with mosses, lichens, and ferns that had absorbed water, sponge-like, later releasing it gradually long after the rain had stopped. Up in the forest canopy, bromeliads had collected rainwater in their
concave leaf bases, forming miniature ponds for numerous tree frogs, salamanders, and hundreds of kinds of aquatic insects. Water, everywhere water, was dripping.
Although I took my time walking through the slick mud, placing each step with care, maybe I should have been daydreaming less. The San Ramon forest contains thousands of insect species, many of them still new and undiscovered, but unfortunately, it also contains lots of venomous snakes and some deadly ones as well—and like Indiana Jones, I hate snakes. Even so, I was enjoying myself immensely, finding fascinating plants and insects all around. Then unexpectedly, just past a bend, down a gentle slope near a small gurgling stream, I came across a small melastome tree. There, on a large leaf about four feet off the ground, I found my time machine. It was about three inches long and deep mahogany brown, with long curved antennae adorned with dewdrops from the recent rain. Standing motionless on the leaf, it rested securely, supported by its six multijointed legs that formed two perfect tripods. My time machine was a long-horned beetle.
As the rain began to fall more heavily at San Ramon, new beads of water started dripping from the beetle. Its tough armored exterior would not allow them to penetrate. The beetle’s body plan is extremely different from our own, with its rigid skeleton on the outside rather than the inside, and this external skeleton, as well as the beetle’s multijointed legs, send us a message from the shallow oceans of the Cambrian period, roughly 541 million years ago. Atmospheric oxygen levels increased at that time, animal metabolism accelerated, and marine predators became faster and nastier. In response, the common ancestor of all living arthropods (insects and their nearest relatives) evolved external skeletons, which provide protection from the environment, defense against predators, and sites of muscle attachment that increase mobility. They evolved jointed legs as well, which are also exceptionally useful for defending against predators, as well as for food-gathering, mating, and dispersal. Both features have been quite fashionable ever since.
The beetle remained motionless on the melastome leaf, but on close inspection I noticed that its abdominal body segments were contracting then expanding slightly. The beetle was breathing. Along the sides of its body, minute holes (spiracles) allowed molecules of air to rush in. If we could shrink ourselves down to the size of a few microns,
we might follow those oxygen molecules on their travels through the beetle’s spiracles, through a series of large tubes (tracheae), and finally through a series of smaller tubes (tracheoles) that branch out in all directions, and get smaller and smaller until they approach all the living cells in the insect’s body. The fact that the beetle breathes air tells us that in the Silurian period, roughly 444 million years ago, ancestral arthropods first colonized the land and developed air-breathing tracheal respiration systems that have been passed onwards to all modern insects, even those that live in fresh water and breathe through gills. Their innovative breathing apparatus allowed Silurian arthropods to exit the oceans to avoid marine predators, forage for food along the shorelines, and use those unoccupied beaches as a safe place to mate and lay eggs. It also prepositioned the arthropods to be the first animal group to successfully diversify among the earliest Lilliputian plant communities, which developed during the Late Silurian.
I examined the beetle’s form more closely. Its body was divided into three functional regions: a head up front, from which its hornlike antennae swept to the sides, and small multifaceted eyes gazed back at me; a central thorax, to which its legs were attached; and lastly, a multisegmented abdomen. These are the features that define an insect. They evolved sometime in the Late Silurian or Early Devonian, about 419 million years ago. During this time, plant communities became taller and more diverse, the first insects evolved among the mossy soils at the bases of the first archaic trees, and six-leggedness established itself as a versatile and stable means of walking, standing, and running on this planet, allowing the insects to become highly successful scavengers. By the Late Devonian period, 360 million years ago, springtails, jumping bristletails, and silverfish were abundant among the accumulating litter of decaying plant materials. The feeding activities of these scavengers created and conditioned organic soils, which enabled the earth’s forests to evolve and expand into the interior from the shorelines. With tiny but triumphant steps, microscopic insects marched inland as the plant communities extended their colonization of the continents.
Along the backside of the beetle ran a hairline seam, which indicated the presence of wings: a message from the common ancestor of all flying insects, which first evolved in the Carboniferous period, about 354 million years ago. When the insects invented wings there
were no other flying animals—no birds, bats, pterodactyls, or gliding squirrels—and they completely mastered the air for more than 150 million years before any other organisms evolved the ability to fly or could chase them in the air. The advantage of flight was certainly one of the foremost factors contributing to the explosive proliferation of insect species on this planet. But wings not only allowed insects to disperse and colonize distant new habitats, they also played important roles in courtship and mating, predator avoidance, food acquisition, and thermoregulation. By the late Carboniferous Period, tall forests had spread across the Earth’s continents. They were a glittering fairyland of curious flying insects: banded, spotted, and net-winged paleodicytoperans; dragonfly-like griffenflies and protodonatans; ancestral mayflies; and even sundry forms of flying roaches that fluttered and glided among the treetops.