Sex on Six Legs Read online

  Sex on Six Legs

  Lessons on Life, Love, and Language from The Insect World

  Marlene Zuk

  Table of Contents

  Title Page

  Table of Contents

  Copyright

  Introduction

  Chapter 1

  Chapter 2

  Chapter 3

  Chapter 4

  Chapter 5

  Chapter 6

  Chapter 7

  Chapter 8

  Chapter 9

  Acknowledgments

  References

  Index

  Copyright © 2011 by Marlene Zuk

  All rights reserved

  For information about permission to reproduce

  selections from this book, write to Permissions,

  Houghton Mifflin Harcourt Publishing Company,

  215 Park Avenue South, New York, New York 10003.

  www.hmhbooks.com

  Library of Congress Cataloging-in-Publication Data

  Zuk, M. (Marlene)

  Sex on six legs / Marlene Zuk.

  p. cm.

  ISBN 978-0-15-101373-9

  1. Insects—Behavior. 2. Insects—Sexual behavior.

  I. Title.

  QL496.Z85 2011

  595.715—dc22 2010025829

  Book design by Melissa Lotfy

  Printed in the United States of America

  DOC 10 9 8 7 6 5 4 3 2 1

  Lines from The Lives and Times of Archy and

  Mehitabel by Don Marquis, copyright © 1927,

  1930, 1933, 1935, 1950 by Doubleday, a division

  of Random House, Inc. Used by permission of

  Doubleday, a Division of Random House, Inc.

  Introduction

  Life on Six Legs

  Two-legged creatures we are supposed to love as we love ourselves. The four-legged, also, can come to seem pretty important. But six legs are too many from the human standpoint.

  —JOSEPH W. KRUTCH

  PEOPLE are more afraid of insects than they are of dying, at least if you believe a 1973 survey published in The Book of Lists. Only public speaking and heights exceeded the six-legged as sources of fear, although "financial problems" and "deep water" (presumably when one was immersed in it) tied with insects at number three. Dying came in at number six. I have no reason to expect that matters have changed much, and suspect that if spiders had been included with insects in the options, fear of the multilegged would have easily topped the chart. People have strong feelings about insects, and most of those feelings are negative.

  And yet for centuries, some of the greatest minds in science have drawn inspiration from studying some of the smallest minds on earth. From Jean Henri Fabre to Charles Darwin to E. O. Wilson, naturalists have been fascinated by the lives of six-legged creatures that seem both frighteningly alien and uncannily familiar. Beetles and earwigs take care of their young, fireflies and crickets flash and chirp for mates, and ants construct elaborate societies, with internal politics that put the U.S. Congress to shame. And scientists—along with many backyard naturalists—keep on wanting to tell their stories.

  It's not just that we publish scholarly journal articles about insects, or use them in our laboratories. Insects are special. Rats and mice are useful scientific tools, too, but although we personify them in fairy tales or cartoons, rodents are just not as compelling as bugs. Birds are beautiful, and we admire them and write poetry about their song and grace, but they don't get under our skin—literally or figuratively—the way that insects do. When it comes to insects, we write about Life on a Little-Known Planet, with Bugs in the System. We muse about Little Creatures Who Run the World, and we're only partly joking. Those of us who study insects are passionate about them in a way that can seem incomprehensible to outsiders. People get why Jane Goodall loves chimps; they are less sanguine about my fondness for earwigs.

  Some of it, of course, is the sheer magnitude of almost everything about insects—they are more numerous than any other animal, making up over 80 percent of all species. Estimates of the number of kinds of insects vary wildly, because new ones are being discovered all the time, but there are at least a million, possibly as many as ten million, which means that you could have an "Insect of the Month" calendar and not need to re-use a species for well over eighty thousand years. Take that, pandas and kittens! At any one moment, say while you are reading this sentence, approximately ten quintillion (10,000,000,000,000,000,000) individual insects surround you in the world. All of that variety gives enormous scope for evolution to act upon. Think of all those species as possible ingredients for a menu in a vast natural restaurant. You can come up with a lot more living recipes with insects than with the paltry few thousand bird species out there. And then there is the sensationalism; nothing gets my students' attention like hearing about male honeybees' genitals exploding after sex, and everyone has shuddered over the female mantis eating her mate. Insects routinely do things that would put the most gruesome horror film to shame.

  Of course, not everyone finds insects scary, The Book of Lists survey notwithstanding. Those books on insects find readers, the nature channels on TV often feature bugs, and in 2009 the London Zoo hosted a "Pestival," "celebrating insects in art, and the art of being an insect." It included art, lectures, discussions, and a celebration of all things entomological. It even featured a six-legged take on the recent death of pop star Michael Jackson: Japanese artist Noboru Tsubaki made a "Vegetable Wasp," described as "a kind of cocoon for Jackson to enable him to traverse between the world of the living and the dead." Whether this effort successfully put Jackson's spirit to rest or not, metamorphosis is a powerful, and not unwelcome, image for us noninsects to contemplate. When Isabella Rossellini made Green Porno, her series of short films on animal mating, she led off with insects: dragonfly, bee, mantis, housefly. They were compelling in a way that other animals are not.

  So what is it that keeps us coming back to insects? Why do they inspire such strong emotions, and what can we learn about ourselves from watching their joint-legged lives? The newest discoveries in biology, about genomes and nerve cells and the evolutionary connections between them, are best revealed by insects. This book is my celebration of a world that is alien and familiar at the same time, an invitation to the latest news about insect lives. We are continuing to make extraordinary and important discoveries about insects, routinely even finding new species. I haven't seen Green Porno, but if the segment on dragonflies is up to date, it should include a shot of the male's jagged penis as it scoops out the sperm from a previous mate, replacing it with his own. Sperm competition, in which the sperm of multiple males battle inside a female's reproductive tract, was first discovered, and is best understood, in insects, and new aspects of it are being uncovered all the time.

  Insects are even teaching us about mind control, and maybe even about consciousness itself. A tiny wasp called the emerald cockroach wasp can do what many renters cannot: direct the movements of a cockroach. The wasp does this not to rid a kitchen of scuttling invaders but to feed her brood. Many wasps provision their young by paralyzing other insects or spiders and carrying them back to the wasp's nest. The paralysis, as opposed to out and out killing of the prey, helps the prey stay fresh while the young wasp larva feasts on the flesh. Of course, paralyzed insects can't put themselves into the nest, so the wasp usually has to do all the heavy lifting, staggering under the weight of her groceries as she flies back to her young. Except, that is, in the case of the jewel wasp, so named for the glittery emerald sheen of her exoskeleton. The female wasp doesn't send the roach into an immobile stupor; instead, she makes it into a zombie via a judicious sting inside the roach's head, so that its nervous system, and legs, still function well enough to allow it to
walk on its own. Then, as science writer Carl Zimmer describes, "The wasp takes hold of one of the roach's antennae and leads it, like a dog on a leash, to its doom."

  For years scientists were mystified about the precision of this sinister manipulation of the nervous system. How could a single injection of venom manage to produce what neuroscientists Ram Gal and Frederic Libersat, from Ben-Gurion University of the Negev in Israel and the Université de la Méditerranée in France, called "a living yet docile" victim? Finally, in 2010, through a series of meticulous manipulations of the cockroach nervous system, including a kind of wasp-mimicking injection at various sites along the collections of nerve cells in the head, the researchers demonstrated that the drive to walk in response to most stimuli is seated in a tiny cluster of cells called the subesophageal ganglia. By poisoning just this minuscule part of the nervous system, the wasp is able, in Gal and Libersat's words, "to 'hijack the cockroach's free will.'" Zimmer refers to the discovery as finding "the seat of the cockroach soul." I am not so sure I buy the idea that roaches have souls to be found, nor that free will is residing in all those cockroaches lucky enough to miss an encounter with a jewel wasp, but then I am not sure about either of those things in humans, either. But the finding illustrates one of the most enthralling aspects of insects: they make difficult-to-grasp concepts, for example, souls and free will, satisfyingly literal. If we can get to a roach's motivation to walk by throwing a monkey wrench into a couple of cells, can the ability to find motivations for human behaviors be far behind?

  Maybe you are convinced that insects are important simply because they invade our kitchens and crops, but you don't think they have any inherent magic. If you are one of those that think insects are important but not breathtaking, pests without inspiring passion, I want to change your mind. It's not just that insects are useful, even essential, given their role in pollination—providing what are now trendily called ecosystem services —or the use of their genetic information to cure malaria. Those practical reasons can make you need something, but not love it; no one denies our reliance on, say, soap, or drywall, but who wants to hear about their intricacies? Insects, on the other hand, can help us see another way of life, like a gloriously overblown version of cultural exchange. Travel is said to be broadening because it makes us realize that our way of doing things is not the only one, that people in other cultures live differently and get by just fine. Insects do that, too, only better. They too make us see that our way of life is not the only one—and I don't mean that we could be eating dung instead of cheeseburgers. I mean that it is possible to be unselfish without a moral code, sophisticated without an education, and beautiful wearing a skeleton on the outside. Insects can shake you in ways you never expected, and even more new discoveries about their lives have been made possible just in the last few years by the tools of genomics. So what do insects have that people haven't noticed?

  Insects Are Equal Opportunity

  INSECTS are the great equalizers. There is not a corner of the globe where people—rich, poor, old, or young—have not had some encounter with insects, even if only to swat a mosquito or crush a cockroach. Because of that ubiquity, insects are the easiest portal to the animal kingdom, an inadvertent reminder that other creatures live here besides us, whether we want them to or not. We are all in the same buzzing, crawling boat.

  But this is not to bemoan that we are all dragged down by the assault of six-legged life on our crops or our persons, a kind of vermin-ridden misery loves company. Insects also provide a much more uplifting egalitarianism. If you want to learn about the natural world but are too young or too poor or otherwise lack an opportunity to study the stars or put droplets of pond scum under a microscope, bugs are always there for you. I grew up in the middle of Los Angeles in a modest neighborhood without creeks or woods or much in the way of encouragement to do a project for the science fair. But early on I discovered that if I lifted the hexagonal concrete pavers in the yard, ants would rush to and fro carrying their plump white pupae, and that the tiny spiky monsters on the rosebush would metamorphose into ladybugs. I reared the fritillary butterflies that lived on a passionflower vine in our yard, year after year, never tiring of watching as the eggs hatched into threadlike caterpillars that grew and grew inside my jars, eventually hanging upside down from a stick and becoming a gaudy spangled adult. No special equipment necessary, no need to venture anywhere my mother would disapprove of or that cost any money at all. And the results were just as compelling, maybe more so, than if I'd had a telescope or a dissecting kit or a way to watch the social lives of wolves.

  This equal-opportunity entomology has been going on for centuries. Maria Sibylla Merian was a German-born painter whose work is rediscovered and shown every few decades; she was recently featured at the Getty Museum in Los Angeles. Merian documented, many years before the naturalists of the time, the life cycles of butterflies, moths, and other insects. Her work is exquisite from an aesthetic perspective, but what interests me more is that as a woman in the late seventeenth and early eighteenth centuries, she was able to make scientific contributions that would have been impossible in virtually any other field, simply by virtue of using the specimens from her own garden. She eventually traveled to Surinam to study the brilliantly colored insects of the steamy jungle, but that was after her interests had been firmly set. Although she, like many other women scientists and naturalists, faced opposition for her unfeminine activities, the accessibility of her subjects meant that she could keep doing the work she loved.

  Interestingly, professional entomology has become one of the more male-dominated fields of biology, perhaps because of its connections with crop pest management and agribusiness, both of which tend to attract men. Regardless, it still appeals to children, both boys and girls, as my experience testifies. And even now it is not impossible to make important discoveries without a lot of technological gizmos. A group of scientists working in Brazil recently discovered that caterpillars parasitized by a wasp continue to make an unwitting sacrifice even after the wasp larvae have emerged from their host to pupate on a nearby stem. The ravaged caterpillar stands guard over the developing wasps and defends them against intruders with vigorous swings of its body, a most uncaterpillar-like behavior. Apparently the wasps exert a kind of mind control over their host that persists even after they leave it, doomed to die before it will ever become a moth.

  This gruesome story has many arresting elements; most of the news coverage used words such as voodoo and zombie, as with the jewel wasp mentioned above. What I like most about it is that the scientists who discovered it were just watching the goings-on in a guava plantation, an illustration of what you can find if you are just paying attention. High tech has its place, of course, and I would hardly champion a return to simpler science or the eschewing of DNA sequencers. But I take great pleasure in the unifying ability of studying bugs. It's not just that insects level the playing field: they even supply the toys. The chapters that follow will let you play with them, will let you in on some remarkable new truths, in a way that would be impossible with most other fields of science.

  Insects Are a Mirror

  ALONG with all of their alien behavior, insects seem to do much of what people do: they meet, mate, fight, and part, and they do so with what looks like love or animosity. Dung beetles take care of their helpless squirming young, doing almost everything human mothers do, short of giving their baby a bottle—or parking it in front of the television. Ants keep aphid "cattle," moving their herd from place to place and milking the honeydew the aphids produce. Bees convey the location of food using symbols. Unlike any other nonhuman animal, some insects live in sophisticated hierarchical societies, with specialized tasks assigned to different individuals and an ability to make collective decisions that favor the common good. They mirror most of our familiar behaviors.

  And yet they do all those things in stunningly different ways from humans, getting to what look like the same destinations without any of the same highw
ay systems or modes of transport. That reflection we recognize is eerily superficial, because what drives the behaviors is not what drives our own. Underneath the maternal care, the language, the system of social favors given and returned is a handful of nerve cells casually strung together in a few small clusters along the body wall. No cerebrum, no right and left hemispheres, not even that so-called reptilian brain part, the cerebellum. They don't have a pituitary gland, or a system of hormones like ours. And yet a sphecid wasp with a body smaller than a kidney bean can dig a burrow in the sand, go off to find a caterpillar just the right size to feed her young, and bring it back to the burrow, remembering where it was and how many other caterpillars she had already brought there. Most of us couldn't find a single caterpillar if we were commanded to do so, much less bring it back to a site the equivalent of a county away. A whole ant colony, with all the drama of the queen suppressing the reproduction of her daughters, can live inside an acorn. A female insect can survey an array of frantically displaying males, select one on the basis of a tiny difference in song, color, or smell, and then store his sperm for weeks or even years before selectively using a particular mate's DNA to fertilize some—and only some—of her eggs.

  How is that possible? How can you get what looks like human reasoning, even human love, when you lack not only a human brain but even the chemicals in the blood that drive human emotions? It is easy to endow a fellow warm-blooded creature, for example, a dog or a bird, with motivations and feelings like our own, harder to do so when the entire nervous system of a fruit fly producing a wing-fluttering courtship song of come-hither would fit on a sesame seed.

  Insects bring home the uneasy truth that you don't need a big brain to do big things, and that in turn makes us question how the mind and, dare to say it, the spirit, are related to the brain. It even makes us question what it means to be human. What does it mean to have complex behavior? Does it mean you are smart? Is the complexity of a honeybee nest with its exquisitely economical hexagons equal to that of a Park Avenue brownstone? We all have our prejudices, and even scientists can be terribly vertebrate centric about understanding behavior. A huge fuss is made about the behavioral flexibility it takes for a New Caledonian crow to construct a tool from a leaf to poke a grub out of a branch, or a chimp to use a stick to get termites from a hole in the ground. It's that flexibility, we say, that's important—humans and a few other anointed species can change what they do to suit changing circumstances. We aren't little automatons; we are unique individuals. Behavioral flexibility is taken as the hallmark of intelligence and hence the key to human evolution. It is often linked to brain size, and that in turn is said to be important for allowing our complex behavior.