Built by Animals To Graeme Built by Animals The natural history of animal architecture MIKE HANSELL 1 3 Great Clarendon Street, Oxford OX2 6DP Oxford University Press is a department of the University of Oxford. It furthers the University’s objective of excellence in research, scholarship, and education by publishing worldwide in Oxford New York Auckland Cape Town Dar es Salaam Hong Kong Karachi Kuala Lumpur Madrid Melbourne Mexico City Nairobi New Delhi Shanghai Taipei Toronto With offices in Argentina Austria Brazil Chile Czech Republic France Greece Guatemala Hungary Italy Japan Poland Portugal Singapore South Korea Switzerland Thailand Turkey Ukraine Vietnam Oxford is a registered trademark of Oxford University Press in the UK and in certain other countries Published in the United States by Oxford University Press Inc., New York © Mike Hansell 2007 The moral rights of the author have been asserted Database right Oxford University Press (maker) First published 2007 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press, or as expressly permitted by law, or under terms agreed with the appropriate reprographics rights organization. Enquiries concerning reproduction outside the scope of the above should be sent to the Rights Department, Oxford University Press, at the address above You must not circulate this book in any other binding or cover and you must impose the same condition on any acquirer British Library Cataloguing in Publication Data Data available Library of Congress Cataloging in Publication Data Data available Typeset by SPI Publisher Services, Pondicherry, India Printed in Great Britain on acid-free paper by Biddles Ltd., King’s Lynn, Norfolk ISBN 978–0–19–920556–1 13579108642 Contents List of Figures vi Preface vii 1. The Builders 1 2. Builders Change the World 26 3. You Don’t Need Brains to be a Builder 58 4. Who’s in Charge Round Here? 92 5. From One Nest to Another 121 6. Two Routes Lead to Trap Building 147 7. The Magic of the Tool Users 180 8. Beautiful Bowers? 216 Notes and References 252 Index 258 v List of Figures 1.1 Brants’ whistling rat burrow system 16 1.2 Nest of long-billed spiderhunter 20 1.3 Leafcutter ants’ nest 23 2.1 Mud shrimp burrow 35 2.2 Magnetic termite nests 44 3.1 Amoeba case 59 3.2 Similar beaks, dissimilar nests 65 3.3 Beaks indicate feeding habits 66 3.4 Oikopleura house 70 3.5 Which species are burrow diggers? 88 4.1 Virtual wasp nests 118 5.1 Cliff swallow nests 124 5.2 A history of nest building 126 6.1 Araneus spider’s orb web 151 6.2 Marine worm web 158 6.3 Amino acids in spider silk 164 6.4 Silk absorbs energy 169 7.1 Chimpanzee passes the trap-tube test 194 7.2 Tool use by a capuchin monkey 197 7.3 New Caledonian crow makes tools 200 8.1 Avenue display of the spotted bowerbird 217 8.2 Golden bowerbird on its bower 221 vi Preface It is a family story, and therefore probably untrue, that when at the age of about six I went missing on my short walk to school, I was eventually found watching a beetle negotiating the gutter. My first natural history enthusiasm was certainly insects. Later, an under- graduate project on the case-building behaviour of caddisfly larvae led to a doctoral thesis on the same subject. By that time I knew more than most people would wish to know about caddis larval cases. Leaving them completely behind, I spent two years teaching at the University of Khartoum in the Sudan, returning to the UK as an Assistant Lecturer at the University of Glasgow in 1968. On arriving there I was asked to give three lectures that probably changed the direction of my career. At that time, Glasgow final-year Zoology students were given, apart from their special subject lectures, a series of occasional lectures called the ‘A Course’. This in essence consisted of a handful of us aca- demics each giving a few lectures on whatever took our fancy. Three lectures on caddis cases seemed excessive, so I decided to go to the other extreme and talk about everything that was built by whatever animal. This, I decided, was not to be a mere parade through the animal kingdom but an attempt to make some sense of, and discover some pattern in, the behaviour of that miscellaneous bunch of web spinners, house, case, mound, and nest builders. That is what I have tried to do ever since, and this book is an attempt to explain that biology, the biology of animal architecture and building behaviour, to anyone to whom that sounds appealing. It is a book about who builds, how they build and what those buildings do. It touches upon environmental impact, animal intelligence, architecture, engineering vii Preface and building materials, on the organization of workforces, on traps, tools and art. Writing this book has not been the lonely experience that some authors complain about. I would like to thank all those colleagues and friends who, through their daily interest and encouragement, contributed to its completion. This is my first experience of writ- ing for a non-specialist audience, so I am very grateful to Lorna and Rowland Mitchell who, in the role of general readers, gave me valuable feedback, and to Jacquie Marshall who read and tact- fully commented on the whole text. For specialist biological infor- mation and advice, I would like to thank Martin Burns, Robin Dunbar, Geoff Hancock, Felicity Huntingford, Bob Jeanne, Bill McGrew, Aubrey Manning, Maggie Reilly, John Riddell, Flavio Roces, Douglas Russell and Richard Wrangham. For very helpful information on human architecture, I must thank Jonathan Hale. For an enjoyable adventure to find the church of All Saints, Little Shelford, my thanks to Martha Jennings. Finally, I want to express my enormous appreciation to Graeme Ruxton. His broad interests, his enthusiasm, and his readiness to sit down and discuss points of biology have contributed immeasurably to the development of the final text. He was not only prepared to read everything but also read again my revised drafts. I dedicate this book to him. viii 1 The Builders Standing with its back to the Atlantic atop a 90m (nearly 300ft) vertical cliff, at the base of which the ocean seethes and foams, is the great semi-circular, prehistoric fort of Dun Aengus. The location is the very westernmost fringe of Europe, the Aran Islands off the coast of Ireland. On the landward side, the fort’s protection from attack is man-made. The half-moon inner sanctuary of the fort (45m or 148ft across) is embraced by a drystone rampart reaching over 5m high and nearly 4m thick. Beyond this are a further three irregular semi- circles of defensive walls and, should even the outer one be overrun, the attackers must then negotiate a field of massive limestone shards, jagged and stood on end. This is a chevaux-de-frise, a term also used to describe the barbed-wire enlargements that protected First World War trenches, but literally ‘horses of Friesland’, spiked obstacles used at least from the seventeenth century to break up cavalry charges. The age of Dun Aengus is uncertain, although it is probably over 2,000 years old: more surprisingly, we still do not know what threat could have stimulated the building of such formidable defences. Our need for protection is not any different from that of other species. Animals have always had enemies, in particular the climate, and other species seeking to prey upon them. We are just a newcomer species resorting to building to protect ourselves in a threatening world which includes 1 The Builders our fellow humans among our enemies, and we are not the first species to make use of a chevaux-de-frise. Think of the dangers that beset insects in a tropical environment. Probably the two greatest are predation by birds and by ants. The hairiness of some caterpillars is a defence against one or both of these, but ultimately the caterpillar must become an adult butterfly or moth. This requires a radical reorganization in its body design— crawling around eating leaves is replaced by flight, nectar feeding and mating. This transition can only be accomplished as an immobile, and therefore vulnerable, pupa. The commercial silkworm typifies the defensive strategy of moth caterpillars. It spins a silken cocoon to enclose itself completely, then it casts off its caterpillar skin to become a pupa from which a moth will later hatch. The silkworm is a hairless caterpillar, but imagine the consequences of a hairy caterpillar pupating inside its cocoon. Not only will it be shedding a hairy skin that crowds the inside of the cocoon, it will also be casting away protection that has already served it well against the threat of ants and even birds. The caterpillar of the moth species Aethria carnicauda, is densely covered in long hairs. When ready to pupate in its native habitat of Central American forests, it selects a straight plant stem as a site to prepare its pupal defences. Facing down the stem, the caterpillar reaches back over its body to pluck out its hairs one by one with its jaws. Each hair in turn is secured to the stem, using the silk thread which is extruded from its mouth. In this way, the caterpillar builds up a disc of radiating bristles, a barrier to anything trying to pass up the stem.