How Insects Work: An Illustrated Guide to the Wonders of Form and Function from Antennae to Wings

Contents

Cover

Copyright

Contents

Introduction

1. Ancestors and Evolution

1.1 Rise of the arthropods

1.2 The first insects?

1.3 The first fliers

1.4 Insect evolutionary tree

1.5 Carboniferous Earth: A land of giants

1.6 Recent evolution

2. The Insect Body-Plan

2.1 Exoskeleton

2.2 The three body-sections

2.3 Segmentation and appendages

2.4 Limb structure

2.5 The wings and elytra

2.6 Unusual bodies

3. The Senses and the Nervous System

3.1 Eyes

3.2 Antennae

3.3 Chemoreception

3.4 Hearing, touch, and more

3.5 Brains, ganglia, and nerves

3.6 Insect intelligence

4. Movement

4.1 Muscular system

4.2 Movement on land

4.3 Flight

4.4 Swimming and diving

4.5 Escaping danger

4.6 Immobility

5. Feeding and Digestion

5.1 Mouthpart anatomy

5.2 Types of diet

5.3 The digestive tract

5.4 Processing food

5.5 Changes during life cycle

5.6 Drinking and fluid balance

6. The Respiratory and Circulatory Systems

6.1 Breathing system

6.2 Gas exchange

6.3 Circulatory system

6.4 Hemolymph

6.5 Unusual adaptations

6.6 Hormones

7. The Reproductive System

7.1 Male reproductive anatomy

7.2 Female reproductive anatomy

7.3 Mating and fertilization

7.4 Parthenogenesis

7.5 Laying eggs

7.6 Unusual adaptations

8. Eggs and Larvae

8.1 Types of eggs

8.2 Development in the egg

8.3 Types of larvae

8.4 Feeding

8.5 Growth and molt

8.6 Lifestyle changes

9. Metamorphosis

9.1 Types of life cycle

9.2 Incomplete metamorphosis

9.3 Full metamorphosis

9.4 Transformation within the pupa

9.5 Emergence

9.6 Maturation in adulthood

10. Behavior and Anatomy

10.1 Feeding behavior

10.2 Breeding behavior

10.3 Parental care

10.4 Seasonal behavior

10.5 Eusocial insects

10.6 Interspecies interactions

11. Cells and Biochemistry

11.1 Structure of a typical cell

11.2 Cell organelles

11.3 Cell replication

11.4 Immunology

11.5 Specialized cell types

11.6 Insects in cellular research

12. Diversity and Conservation

12.1 Types of insects

12.2 Insect communities in different habitats

12.3 Record-breakers

12.4 Threats facing insects

12.5 Extinction

12.6 Insect conservation

Glossary

Index

Photo credits

About the Author

How Insects Work:

An Illustrated Guide to the Wonders of Form and Function—from Antennae to Wings

Copyright © 2020 by UniPress Books Limited

The credits page is a continuation of this copyright page.

Published in North America by The Experiment, LLC, in 2020.

All rights reserved. Except for brief passages quoted in newspaper, magazine, radio, television, or online reviews, no portion of this book may be reproduced, distributed, or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or information storage or retrieval system, without the prior written permission of the publisher.

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Library of Congress Cataloging-in-Publication Data

Names: Taylor, Marianne, 1972- author.

Title: How insects work : an illustrated guide to the wonders of form and function-from antennae to wings / Marianne Taylor.

Other titles: How nature works.

Description: New York City : The Experiment, 2020. | Series: How nature works | Includes index.

Identifiers: LCCN 2019056118 (print) | LCCN 2019056119 (ebook)

Subjects: LCSH: Insects--Anatomy.

Classification: LCC QL494 .T39 2020 (print) | LCC QL494 (ebook) | DDC 595.7--dc23

LC record available at https://lccn.loc.gov/2019056118

LC ebook record available at https://lccn.loc.gov/2019056119

Ebook ISBN 978-1-61519-650-0

Conceived, designed, and produced by UniPress Books Limited

unipressbooks.com

Cover design by Beth Bugler

Contents

Introduction

1

ANCESTORS AND EVOLUTION

1.1 Rise of the arthropods

1.2 The first insects?

1.3 The first fliers

1.4 Insect evolutionary tree

1.5 Carboniferous Earth: A land of giants

1.6 Recent evolution

2

THE INSECT BODY-PLAN

2.1 Exoskeleton

2.2 The three body-sections

2.3 Segmentation and appendages

2.4 Limb structure

2.5 The wings and elytra

2.6 Unusual bodies

3

THE SENSES AND THE NERVOUS SYSTEM

3.1 Eyes

3.2 Antennae

3.3 Chemoreception

3.4 Hearing, touch, and more

3.5 Brains, ganglia, and nerves

3.6 Insect intelligence

4

MOVEMENT

4.1 Muscular system

4.2 Movement on land

4.3 Flight

4.4 Swimming and diving

4.5 Escaping danger

4.6 Immobility

5

FEEDING AND DIGESTION

5.1 Mouthpart anatomy

5.2 Types of diet

5.3 The digestive tract

5.4 Processing food

5.5 Changes during life cycle

5.6 Drinking and fluid balance

6

THE RESPIRATORY AND CIRCULATORY SYSTEMS

6.1 Breathing system

6.2 Gas exchange

6.3 Circulatory system

6.4 Hemolymph

6.5 Unusual adaptations

6.6 Hormones

7

THE REPRODUCTIVE SYSTEM

7.1 Male reproductive anatomy

7.2 Female reproductive anatomy

7.3 Mating and fertilization

7.4 Parthenogenesis

7.5 Laying eggs

7.6 Unusual adaptations

8

EGGS AND LARVAE

8.1 Types of eggs

8.2 Development in the egg

8.3 Types of larvae

8.4 Feeding

8.5 Growth and molt

8.6 Lifestyle changes

9

METAMORPHOSIS

9.1 Types of life cycle

9.2 Incomplete metamorphosis

9.3 Full metamorphosis

9.4 Transformation within the pupa

9.5 Emergence

9.6 Maturation in adulthood

10

BEHAVIOR AND ANATOMY

10.1 Feeding behavior

10.2 Breeding behavior

10.3 Parental care

10.4 Seasonal behavior

10.5 Eusocial insects

10.6 Interspecies interactions

11

CELLS AND BIOCHEMISTRY

11.1 Structure of a typical cell

11.2 Cell organelles

11.3 Cell replication

11.4 Immunology

11.5 Specialized cell types

11.6 Insects in cellular research

12

DIVERSITY AND CONSERVATION

12.1 Types of insects

12.2 Insect communities in different habitats

12.3 Record-breakers

12.4 Threats facing insects

12.5 Extinction

12.6 Insect conservation

Glossary

Index

Photo credits

Introduction

Across the great and varied sweep of life on Earth, insects stand out as one of the greatest success stories. Most invertebrate animals live in the oceans and fresh waters, but insects have truly conquered the land, and (as the only winged invertebrates that have ever lived) they have also mastered the air. This mastery comes courtesy of a basic anatomy that meets the challenges of life out of water, and thanks also to countless anatomical modifications that allow insects to thrive in so many different habitats and ecological niches.

For all their fabulous variety, insects have the same fundamental body-plan, which allows them to be recognized at a glance. The segmented body has three distinct sections: the head, the thorax, and the abdomen. There are six legs and (usually) two pairs of wings attached to the thoracic segments, and there are obvious eyes and various sensory and feeding appendages on the head. Whether the insect crawls, runs, climbs, or hangs, whether it flies with a rattling zoom, a buzz, or a flutter, whether it hunts prey, chews leaves, or sucks nectar (or blood), it does so with its own version of the same physical equipment that first evolved more than 350 million years ago.

A spectacular Spiny Flower Mantis exhibits its eye-spot wing markings, to startle a predator.

One of the keys to insects’ success in the open air lies in their outer covering—a waxy cuticle that helps prevent their tiny bodies from dehydrating. To take oxygen from the air, they use spiracles—breathing apertures in the body-segments, which take in air passively and can be opened and closed as needed. Instead of blood contained in vessels, they have free-flowing hemolymph, which helps keep their bodies rigid, aids movement, and assists the transportation of nutrients and waste materials to the appropriate parts of the body. The nervous system is modular—in a sense, each of the body segments has its own individual and autonomous brain—and some other body systems show a similar modularization. These are just a few of the many ways in which insect bodies are structured and function completely differently from our own, though it is the process of complete bodily metamorphosis, from wormlike larva to winged adult, that astounds us most of all.

The male Stag Beetle is a fighting machine—his huge jaws are for wrestling a rival rather than biting.

endless forms most beautiful

There are well over a million species of insects known to science today, and probably many more that are as yet undiscovered. They have adapted to live on every continent and in every kind of environment, fulfilling an array of ecological roles. Some are our constant companions—a few are even domesticated for our use—and others are our sworn enemies, but the vast majority are almost unknown to most of us. This book aims to unravel the mystique of insects—how their bodies work, how they lead their lives, and how deeply and completely the lives of other organisms on Earth (including ourselves) depend on them.

The Madagascan Sunset Moth is noted for its long migrations as well as its dazzling colors.

1

ancestors and evolution

Insects are the most successful and diverse of all land animals. Their long evolutionary history has furnished them with uniquely adaptable bodies, capable of thriving in all environments. They have survived five mass extinctions, and many species have even surmounted the greatest challenge of all—successfully surviving alongside humanity.

1.1 • Rise of the arthropods

1.2 • The first insects?

1.3 • The first fliers

1.4 • Insect evolutionary tree

1.5 • Carboniferous Earth: A land of giants

1.6 • Recent evolution

Trilobites were ancient arthropods and cousins to the insects—their segmented structure has proved an enduringly successful body-plan.

rise of the arthropods

Insects are invertebrate animals belonging to the larger group Arthropoda, meaning jointed feet. Their bodies also have movable joints at certain points on their rigid outer shell.

Humans, along with other mammals and all vertebrates, have an endoskeleton. The strong, rigid framework of bones is inside, with muscles, blood vessels, nerves, and other soft, fleshy structures around them. In insects, this anatomy is reversed. Their structural framework, the exoskeleton, is on the outside and the soft parts are within.

As well as insects, the arthropod group today includes crabs and other crustaceans, spiders and other arachnids, and the many-legged millipedes and centipedes. Their basic body-plan is bilateral symmetry, with left and right as mirror images, and the body is divided into many sections, called segments. The jointed legs and other limbs or appendages are in pairs along each side.

the exoskeleton

The first animal with a segmented exoskeleton and jointed limbs lived more than 540 million years ago, in the sea. Its appearance was a major event in evolution, introducing a very adaptable body arrangement. (An incidental benefit is that a strong, tough exoskeleton was much more likely to be preserved as a fossil—a huge help for our studies today.) The earliest fossil arthropods were small organisms, from the size of rice grains to grapes, and resembled a mix of worm and crustacean. But these remains are vague and difficult to classify.

Fossil trilobites: These early arthropods first appeared on Earth some 521 million years ago.

Modern arthropods like crustaceans (here an isopod) and insects (here a damselfly) both descend from an animal with simple repeated body-segments, each bearing jointed appendages.

Trilobites were swimming arthropods that lived in seas worldwide some 525 million years ago, during the Cambrian Period. The sea scorpions, or eurypterids, formed another prominent arthropod group. These fearsome predators first lived around 460 million years ago, in the Ordovician Period. Some, such as Jaekelopterus, were among the largest arthropods of all time, at 8 feet (2.5m) long. Both trilobites and eurypterids flourished for more than 200 million years, then gradually declined. The last of them died out in the Permian–Triassic mass extinction event, 252 million years ago.

onto land

Meanwhile, other arthropods had moved onto land, probably 430 to 450 million years ago during the Ordovician Period. Their basic body design and anatomy were already well suited to terrestrial life—a feature in evolutionary science known as preadaptation. The tough, impermeable exoskeleton greatly reduced body fluid loss in air, and the jointed limbs held up the body for moving around. Some of the first terrestrial arthropods were trigonotarbids, which were arachnids similar to their modern spider relatives. Mostly small, ⅕ to ⅘ inch (0.5 to 2cm) in length, they went extinct about 290 to 300 million years ago. A very different destiny awaited one of the next arthropod groups to colonize land—the insects.

the first insects?

In the Devonian Period, 359 to 419 million years ago, insects were spreading into early terrestrial habitats, helped along by pioneer plants, which established environments and food sources.

Silverfish have altered little in anatomy since their ancestors first appeared about 380 million years ago.

A single fossil, as small as this o, may be the oldest known insect fossil. The fossil in question is Rhyniognatha hirsti and is the subject of continuing debate. It consists of most of a tiny head but little else. It was excavated in 1919 from flintlike rocks called Rhynie chert, at a village near Aberdeen, Scotland. In 1926 it was interpreted as an arthropod, but as a springtail or collembolan, Rhyniella praecursor, a relative of true insects. In 1928, reexamination, especially of the mandibles—insect jaws—showed it to be a true insect and it was renamed Rhyniognatha hirsti. The specimen is dated to the early Devonian Period, 395 to 400 million years ago.

changing opinions

For decades Rhyniognatha was famous as the very earliest insect fossil. In 2002 it was reexamined using much improved microscopes. The verdict was that its mandibles moved with a scissorlike action, using two joints. This anatomy is found in the mandibles of flying insects, but not in non-fliers, which were assumed to have evolved first. The earliest fossils of flying insects do not appear until at least 70 to 80 million years after Rhyniognatha. So if Rhyniognatha was indeed a flier, this would push back the origins of insect flight many millions of years, and the beginnings of insects in general even further.

The Rhyniognatha specimen itself showed no wings, but this is unsurprising since it was originally preserved in a hot spring where tiny fragile wings were unlikely to survive. These 2002 studies suggested the whole creature resembled a mayfly that could rest on a human fingernail.

not an insect?

In 2017 there was another twist. The Rhyniognatha specimen was examined again using more advanced microscopes, which revealed previously overlooked fragments including additional mouthparts. The new conclusion was that Rhyniognatha was not an insect. The anatomy of the head parts, plus information about other arthropods present in the fossil-dig location at the time, meant it was more likely an early relative of centipedes. Perhaps future generations of microscopes and experts will settle the status of Rhyniognatha.

Firebrats are widespread primitive insects which often occur in hot, humid environments.

Fossils from about 380 million years ago onward, in eastern North America and gradually spreading to Eurasia, are generally accepted as early insects. They were wingless and came from the groups known as Archaeognatha (rock and jumping bristletails) and Zygentoma (silverfish and firebrats). These kinds of insects are known as primitive, which in biology means a form that arose early in evolutionary history and has changed or been modified little since.

The controversial fossilized mandibles of Rhyniognatha hirsti, which was a possible early insect.

It is not the case that evolution has passed them by, merely that environmental conditions that suit their survival have remained in more or less the same state for all those millennia. They have continued to evolve, but only to become better and better at living in the same way that they always have.

STUDYING INSECTS

Our understanding of what insects are made of and how they live their lives is constantly growing, thanks to the efforts of scientists working in labs and wild places all around the world.

The study of insects is called entomology. However, entomology as a field of study draws upon many other disciplines, too, including genetics, cell biology, comparative anatomy, ecology, biogeography, and biochemistry. To understand fully how any given species functions, we need to look not only at its anatomy and cellular structure and its physiological processes during its life cycle, but at how, as a living insect, it uses its environment and how it fits into ecosystems.

Insects lend themselves to study in the lab in many ways, as they are mostly small, easy to keep, and breed rapidly, so it is easy to obtain specimens for tissue samples, and easy to study living processes and behaviors under controlled conditions. Studying the activities of insects in the wild is a very different matter. Even tracking one individual’s movements over more than a few seconds can be impossible, although satellite tagging technology is evolving so rapidly that it