Sex on Six Legs Read online

  Authors write fiction about parallel universes, they ponder the possibility of supernatural beings, maybe even the spirits of the departed, traveling in our midst. The ability to glimpse another world is always touted as an allure for those who dabble in the paranormal. But who needs to be able to see dead people when you can see live insects?

  Chapter 1

  If You're So Smart, Why Aren't You Rich?

  Learning on Six Legs

  THE FAMOUS eighteenth-century naturalist Jean-Henri Fabre meticulously examined the mason bees of his native France, marveling at the tiny clay cells they constructed as cradles for their helpless larvae. When the young bee is ready to emerge, under the normal scheme of things it scissors its way out of the clay with its mandibles and squeezes through the opening. But Fabre, like calculating scientists before and after him, tested the ability of the bees to think by examining how they were able to overcome various manipulations of their chambers. First, he thwarted a bee by removing part of the clay and replacing it with a piece of paper. Undaunted, it sliced through the paper with the same motions it used for the thicker material. Then Fabre presented the young bee with not one, but two barriers: the usual clay, and paper a half inch in front of it, so that the insect needed to repeat the motion it had performed on the original cell on the paper. This it was unable to do, instead tapping fruitlessly at the paper it was completely capable of cutting through. Two barriers are never found in nature, and the bee couldn't perform acts outside its repertoire; we now know that it lacks the kind of neurological GPS ("if a new roadblock appears, repeat steps A through G until you see air") necessary to adapt to altered circumstances. Fabre tut-tutted over the bee's ineptitude, noting, "The insect would have to repeat the act which it has just accomplished, the act which it is not intended to perform more than once in its life; it would, in short, have to make into a double act that which by nature is a single one; and the insect cannot do this, for the sole reason that it has not the wish to. The Mason-bee perishes for lack of the smallest gleam of intelligence."

  Later scientists were equally condescending, noting with belittling superiority that although quite a few kinds of insects can perform remarkable tasks, they cannot learn from experience the way we humans can. In the late nineteenth century, the English physician David Douglas Cunningham was posted to the Indian Medical Service in Calcutta, where in addition to studying the pathology of infectious diseases he made detailed observations of the local flora and fauna, including the many large and easily observed insects. He was prepared to admit that some of the large wasps that provisioned their young with paralyzed caterpillars and other prey possessed something along the lines of what he termed intellect, given their complex behavior. But he was also fond of performing "practical jests" on the wasps. The females built mud nests on many objects, including the pipes in his study, and Lieutenant Colonel Cunningham enjoyed occasionally moving the pipe a foot or two from its original location while a wasp was out foraging for prey. He noted that it was then "amusing to observe the astonishment of its tenant when she returns to find her nest gone, and wanders round in perplexity until it is replaced and joyfully recognized." One could certainly wonder about how hard up for amusement one has to be before taking up playing jokes on wasps, but regardless, the same note of self-satisfaction creeps into Cunningham's writing that is seen in the writings of most of the early naturalists. Not being able to find something after it was moved, or being unable to recognize a novel feature in the environment must mean that insects, regardless of their awe-inspiring abilities to construct elaborate hives and find flowers miles away, are dimwitted at heart.

  But in fact, it is turning out that here too our faith in our uniqueness may be misplaced, and that insects are capable of feats of intelligence that qualitatively, at least, may be quite similar to our own. This finding has many useful implications, from the construction of better computers and robots to a potential cure for brain damage. And it also challenges our ideas about what our own enormous brains might be for.

  Six-Legged Smarts

  THE LIKELIEST candidates for insect intelligence, or at least the first ones to be considered by naturalists, have always been the bees, wasps, and ants. Partly this is because we see them more—in our gardens and kitchens—and they seem to be doing things, such as finding food and taking it back to their nest or hive, that require something resembling reasoning. Partly it is because of the sociability of many species, since we use our own intelligence to interact with each other so much. And partly, I think, it has something to do with the way that such insects use objects in their environment, whether it is to build paper cells from chewed wood pulp or to remove pollen from flowers and cram it into the built-in shopping bags on a bee's leg. Animals that have possessions seem smarter, somehow, which may be a comment on our own valuing of material goods.

  Fabre, Cunningham, and a host of other naturalists paid particular attention to the provisioning wasps and bees. These relatives of yellow jackets and honeybees do not live in social groups with a queen and workers. Instead, once she has mated, a single female searches for prey such as caterpillars or large toothsome spiders. After capturing the item, she stings it so that it is paralyzed but not dead, a kind of suspended animation refrigeration system. She lugs her victim to her nest, which may be a burrow in the soil or a custom-built cell on the surface of an object, as with the pipe-loving butts of Cunningham's "jests," and lays an egg on it. After the egg hatches, the young larva has a ready food supply that won't spoil. Depending on the species, the mother may return many times to add prey to supplement the larder or to lay more eggs in additional chambers.

  While grisly in certain respects, the wasp's behavior undeniably requires two of the prerequisites for intelligence: learning and memory. The mother wasp has to remember where her burrow is, find the correct size and number of prey—in one species, the number of food items brought back to the nest is calibrated to the needs of the hungry waiting larvae—and go back to the correct place. All of this cannot be done purely by rote, because each nest is built anew, each cell provisioned separately, and each prey item puts up a different fight. The wasps seem to use landmarks to find their nests, like remembering where one's house is by recalling the location of the Starbucks at the corner, and if the landmarks are moved, the wasps fly around the area, like the agitated subjects of the jokes played by Cunningham. In their defense, incidentally, one wonders how most of us would do if we suddenly found the aforementioned coffee shop lifted in its entirety off of the block, between one latte and the next, and whether we too wouldn't mill around the area, unable to believe our eyes.

  Even more impressive than the ability of these wasps is that of another species of wasp that exploits the provisioning kind. These parasites do not care about the wasp larvae waiting for their paralyzed meal, but about the caterpillars that are brought to the larder. Instead of going out and hunting down their own prey, the parasitic wasps capitalize on the food brought in by the hunters and lay their own eggs on the item. The problem is that only a very narrow window of opportunity to lay an egg on the caterpillar exists, which is during the time that the caterpillar is being dragged into the nest by the wasp that first captured it. So instead of trusting to luck to find a host at exactly the right moment, the parasitic wasp performs a reconnaissance mission, flying around areas where the provisioning wasps are likely to be digging their nests, an activity that takes quite a long time and is much more apparent than the brief provisioning period. Once a nest-building wasp is detected, the parasitic wasp remembers where the nest is located and keeps that nest site under surveillance, so that she can spot when provisioning occurs, often many days later. Then she slips in and hurriedly lays her own eggs on the caterpillar.

  Yet another species of parasitic wasp lays its eggs on clusters of checkerspot butterfly eggs. The catch here is that the eggs can be successfully parasitized only for the few hours when the checkerspot babies have developed into first-stage larvae but have not
yet broken out of the egg. The wasp circumvents this difficulty by learning where the eggs are ahead of time and then monitoring their progress until they are ready, with some individual wasps finding an egg cluster and then revisiting it for up to three weeks, a substantial portion of the wasp's lifetime.

  The wasps and their relatives among the other social insects are not the only ones that can learn new things. The caterpillars and butterflies the wasps use as prey are also capable of learning, and they can also develop preferences for particular foods, depending on the type of plant on which their mother laid her eggs. Such food snobbery is of more than academic interest, since some pest caterpillars that eat crops, for example, the young of the familiar cabbage white butterfly, can learn to eat new varieties of cruciferous vegetables; planting broccoli in hopes of evading butterflies that grew up eating cauliflower is futile. Interestingly, not all kinds of butterflies can learn to go to one kind of plant rather than another; checkerspots, eastern swallowtails, and a species of Heliconius butterfly all seem to be relative dullards. You can rear them on one kind of plant, but if you try to train them to visit another kind when it's time to lay eggs, the mother butterflies just won't make the switch. Perhaps it's not stupidity so much as brand loyalty, like refusing to accept Pepsi instead of Coke even if the former is on sale.

  Parents often swear that their children are born picky eaters, and that they cannot be taught to prefer healthy snacks. But grasshoppers and their relatives the locusts can be taught to determine the nutritional content of different plants and feed preferentially on the most nourishing ones. In the laboratory, grasshoppers can be fed little cubes of synthetic diet, kind of like the power gels consumed by marathon runners, and the contents of the cubes varied according to the experiment. In one study, groups of locusts were given food lacking either protein or digestible carbohydrates. The experimenters gave one food in a yellow tube and one in a green tube, alternating the association between subjects, and then let the insects feed on a balanced diet for a few days to make sure they didn't become malnourished. Then, the locusts were deprived of food for four hours, a rather long time between meals for the insects, which usually eat more or less nonstop. When the locusts were placed in a test chamber containing yellow and green tubes, but no food, they went to the color associated with the nutrient—either protein or carbs—they had been lacking. This feat is particularly impressive because it isn't just the grasshoppers having some holistic instinct for eating what is good for them, but a learned association between color and a nutritional deficit. Toddlers, take note. Admittedly, the researchers didn't try offering the insects a choice between the hopper equivalent of Twinkies and that of tofu, but then I am not sure quite how one would go about determining what insect junk food would be like.

  Honeybees have long been known to navigate using landmarks and use information from each other to find food, as I discuss below and in another chapter, but a recently discovered ability deserves special mention: they can count. The ability to enumerate objects is considered one of those gold standards of intelligence by scientists, and several kinds of primates, some other mammals such as dolphins and dogs, and psychologist Irene Pepperberg's late African gray parrot, Alex, have been shown to do so. Still, you just don't think about insects in the same breath as you do arithmetic. But scientists Marie Dacke and Mandyam Srinivasan of the Australian National University in Canberra trained the bees to fly down a tunnel toward a food reward, using landmarks set along the walls and floor. To get to the food, the bees couldn't simply memorize the position of the landmarks, because the locations of the landmarks were shifted every 5 minutes. Instead, the bees had to learn that the food could be found at the base of landmark number 1, 2, 3, 4, or 5, depending on the individual experiment. Counting to four was mastered relatively easily, but getting to five proved challenging. Nonetheless, that the bees could generalize to a number at all, rather than simply flying until they saw an object in the same place it had been before, is an extraordinary accomplishment.

  The bees' ability is exciting not only because it helps demolish that boundary of the backbone with regard to intelligence, but because being forced to design the experiments required to demonstrate counting in a creature so different from us makes us strip down our methods to their essentials. Finding out if your three-year-old can count is one thing. But how do you come up with a test for counting, or learning in general, when your subjects can't talk, walk on two legs, point to anything, or even get rewarded with something they want, the way most people can? If we can design ways to study animals with these limitations, maybe it will help us work more effectively to test humans with limited abilities, or even design computer programs that could substitute for the abilities that are lacking.

  Figuring out exactly how to test insect intelligence in a way that is meaningful to them but also tells us something is challenging. Reuven Dukas, a biologist at McMaster University in Canada, has studied learning in a wide variety of insects and thinks we may only be scratching the surface of their abilities. After all, if insects don't learn something, he says, echoing teachers everywhere, "Is it because I'm not a good teacher or because the animal doesn't learn?" It's always hard to know what tasks an animal will be able to perform that we can then generalize to other species. Jan Wessnitzer and colleagues from the University of Edinburgh showed that my favorite insects, crickets, could relocate a particular spot on the floor using objects in a photo along the wall of their experimental arena as landmarks—the best navigational aid was a rather stark landscape that looked like a desert in the American Southwest. The training scheme they used consisted of a floor heated to an uncomfortable temperature except for a single cooler spot that the crickets presumably preferred to stand on. It was called, without comment, the Tennessee Williams paradigm.

  The Face Is Familiar, but What about the Antennae?

  LEARNING about food sources is one thing, since it is a natural behavior on the part of many insects, perhaps particularly honeybees. But scientists are now demonstrating that insects can be taught far more sophisticated tasks, sometimes having no apparent relation to their day-to-day requirements. Recently, for example, Shaowu Zhang and his colleagues trained honeybees to be extraordinarily discriminating in their decision making. The bees were given a reward if they chose a particular pattern on a card, but the "right" choice depended on whether it was morning or afternoon, whether the bees were out visiting flowers or returning to the hive, or a combination of both. The bees took a while to learn their task, but they eventually could make the distinctions, an impressive cognitive feat. Bees from laboratories in both Australia and Germany were tested, and in a happy blow for global diplomacy, turned out to be roughly equal at the task.

  But remembering to choose one visual cue over another pales in comparison to another bee achievement: bees can learn to recognize individual human faces. Adrian Dyer at La Trobe University in Melbourne, Australia, and his colleagues there and at Cambridge University in England rewarded honeybees with a sip of sugar solution if they flew toward a particular image, a technique that has frequently been used by researchers. What was novel was the kind of image in his experiments: a black-and-white photograph of a man from a stock collection, compared with a photo of a different person, the same face upside down, and a drawing. Not all the bees got it right, but those that did could remember an individual face several days after their initial training. Dyer isn't suggesting that the bees actually "know" what they are looking at, or that they spend their days scrutinizing the people around them or developing an attachment to the beekeeper. They can't possibly undergo the same cognitive processes that we do when we recognize each other, given their limited nervous systems. Instead, Dyer believes that the ability is probably related to their skill at distinguishing one flower from another while foraging, something more useful in a bee's life. In other words, a bee that can tell a columbine from a daisy could use the same technique to tell a Roman-nosed individual from a snub-nosed one. Dyer went on t
o demonstrate that honeybees could discriminate among photographs of very similar natural scenes, with images of forests that differed only in the orientation of the branches, an ability that probably makes returning to the hive after a long foraging flight easier to accomplish.

  Regardless of how or why they do it, the bees' capacity to learn to recognize human faces has some important implications. Facial recognition has always been one of those skills thought to require a large brain, and psychologists had even speculated that a special part of the human brain is devoted to just that task. But bees don't have any of the same brain components that humans and other vertebrates do, so such a specialized structure must not be necessary to accomplish the discrimination. As Mandyam Srinivasan said, "Sometimes I wonder what we are doing with two-kilogram brains."

  In addition to further blurring those boundaries between human and insect, there are some practical uses for the discovery. Computerized facial recognition would be a boon to security and crime-fighting agencies, and studying the mechanisms behind the bees' ability might yield insights into how to create such programs. I was seized by the image of a chamber with a bee at airport security, for instance, scrutinizing the faces of passengers to look for matches with photos of known terrorists. Whether this would work better than some of the current efforts is an interesting question.

  Some humans themselves cannot distinguish among human faces, a condition known as prosopagnosia, or face blindness, thought to be due to a genetic defect; one estimate claims that 2.5 percent of the population suffers from some form of it. Some people with prosopagnosia can distinguish individual animals, but not people; Jane Goodall is said to have this form of the disorder. Prosopagnosia can also be present to greater or lesser degrees, so that one can have the disorder under certain circumstances but not others. In severe cases, sufferers cannot recognize their own face in a photograph. It seems to be related to the inability to navigate in the environment, which means that bees might be particularly suitable for using as models for studying the disorder, since of course bees are superstars at locating food sources and remembering nest sites. At the moment, no one has worked out the mechanisms by which the bees learn faces, but if they are linked to the ways in which the bees orient in the wild, understanding the bees' abilities could help people overcome their own face blindness.