9
THE PROBLEM WITH COCKROACHES IS US
You must not fight too often with one enemy or you will teach him all your art of war.
—NAPOLEON BONAPARTE
I am almost convinced (quite contrary to the opinion I started with) that species are not (it is like confessing a murder) immutable.
—CHARLES DARWIN
YOU CAN LEARN to be interested in the insect life around you and realize most of the arthropod species nearby are interesting, poorly studied, and more likely to help control pests than to be them. Or you can go to war. The modern way to wage such war is with chemistry. But be warned: if you decide on a chemical war, the battles are not evenly pitched. Not even close. To each round of new chemicals we apply, the insects we attack respond by evolving via natural selection. The more aggressive the attack, the faster the evolution. Insects evolve faster than we can understand how they have evolved, much less counter. It happens again and again, especially among those pests we try hardest to kill, pests such as the German cockroach (Blattella germanica).
The pesticide chlordane was first used in homes in 1948. It was a wonder pesticide, one so toxic to insects that it was thought to be invincible. By 1951, however, German cockroaches in Corpus Christi, Texas, were resistant to chlordane. In fact, the roaches were a hundred times more resistant to the pesticide than were laboratory strains.1 By 1966, some German cockroaches had evolved resistance to malathion, diazinon, and fenthion. Soon thereafter, German cockroaches were discovered that were fully resistant to DDT. Each time a new pesticide was invented, it was just a few years, or sometimes just a few months, before some population of German cockroaches evolved resistance. Sometimes, resistance to an old pesticide would even confer resistance to a new pesticide. In those cases, the battle was over before it even started.2 Once they evolved, resistant strains of cockroaches would spread and, so long as the pesticide continued to be used, thrive.3
Each of these tit-for-tat responses of cockroaches to our sinister chemical ingenuity was impressive. Lineages of cockroaches were rapidly evolving entirely new ways to avoid, process, or even take advantage of our poisons. But these responses were nothing compared to what was recently discovered in the building next to my office. The story of that discovery began more than twenty years earlier on the other side of the country, in California, where it involved two main protagonists: an entomologist named Jules Silverman and a family of German cockroaches named “T164.”
Jules was tasked with studying German cockroaches. He was working at the Clorox Company Technical Center in Pleasanton, California.4 The place was like any other science-based industry, except that what rolled off of the assembly line wasn’t chocolates but devices and chemicals for killing animals. Jules focused on killing cockroaches, especially German cockroaches. German cockroaches are just one of many species of cockroaches that have moved into homes to live alongside humans. As one cockroach specialist reeled off to me at a meeting, “You’ve got your American cockroaches, Oriental cockroaches, Japanese cockroaches, smoky-brown cockroaches, brown cockroaches, Australian cockroaches, brown-banded cockroaches, and, well, quite a few more.”5 Most of the thousands of cockroach species on Earth do not and cannot thrive in homes,6 but this dirty dozen seems to have abilities that predispose them to thrive indoors. Several of these species, for instance, can reproduce parthenogenetically:7 a female cockroach can produce female offspring without any help from a male.8 Though each of the cockroach species that can be found indoors has some adaptation aiding it in life with humans, the German cockroach has the complete package.
When a German cockroach finds itself in the wild, it is a weakling. It is eaten. It dies of hunger. Its young are blighted, afflicted, and unsuccessful. As a result, there are no wild populations of German cockroaches—not anywhere. The German cockroach is only strong and fecund in our presence, indoors. Perhaps this is one of the reasons we have come to dislike them so very much. They like the conditions—warm, not too dry, not too wet—we like. They like the foods we like.9 They can, like us, even suffer from loneliness.10 Whatever the reason we don’t like them, we really don’t have that much to fear from them. German cockroaches can carry pathogens, it is true, but not any more so than your neighbors or children carry them. Also, no cases have yet been documented in which someone has actually gotten sick from a pathogen spread by a cockroach, whereas people get sick every minute of every day from pathogens spread by other humans. The most serious problem posed by German cockroaches is that they are, in great densities, a source of allergens. In response to this real problem, and the many perceived problems, we have spent enormous resources trying to kill German cockroaches.
Just when our battles with German cockroaches began is hard to say because the dead bodies of cockroaches do not hold up well in archaeological sites (at least when compared to those of beetles). Also, people tend to study how to kill German cockroaches rather than the other details of their biology. The closest known relatives of German cockroaches are two species of Asian cockroaches, both of which live primarily outdoors. These two species fly well, feed on leaf litter and other insects, and, in some places, are regarded by farmers and scientists as beneficial agricultural insects.11 Originally, the German cockroach was probably like these wild cockroaches. Then it moved in with humans.12 When it did, it abandoned flying, began to reproduce more rapidly and live more gregariously, and adapted in other ways so as to be most successful in those conditions most preferred by humans. Then it spread.
The German cockroach appears to have made its way through Europe during the Seven Years War (1756–1763), a time when people were traversing Europe with containers large enough to hold quite a few cockroaches. Just who moved the German cockroach around is unknown.13 The father of modern taxonomy, Carl Linnaeus, asserted it was the Germans. Linnaeus was Swedish. The Swedes fought against the Germanic Prussians, so Linnaeus thought that “German cockroach” seemed a fitting moniker for a species that even he didn’t like.14 By 1854, the German cockroach was in New York City. It now lives from Alaska to Antarctica, having moved with peoples of nearly every nation and their boats, cars, and planes.15 It is surprising German cockroaches aren’t yet on the space station.
In places where the temperature and humidity of homes and transport vehicles still vary with the seasons, the German cockroach coexists in homes with other cockroach species,16 some of which (such as the American cockroach) may have associated with our lineage since the days we lived in caves.17 But in dwellings in which humans have invested in central cooling and heating, the German cockroach comes to dominate. Other cockroaches, in response, tend to become rare. Until recently, for example, the German cockroach was uncommon in much of China, but as China began to heat its transport trucks in the north (where it is cold), the conditions in those trucks became warm enough for the German cockroach and it moved north. When China began to cool its trucks in the south (where it is hot), the trucks became cool enough for the German cockroach and it moved south. Having arrived, the German cockroach now finds enough heated apartments in the north and cooled apartments in the south to thrive. Throughout China, and around much of the rest of the globe, as more apartment and house dwellers have invested in central cooling and heating, the German cockroach has become ever more widespread and abundant.18
By the time Jules Silverman started work at the Clorox Company twenty-five years ago, populations of the German cockroach were already on the rise. Jules’s job was to develop new chemicals to kill German cockroaches. The best thing on the market at the time was roach bait. You know roach baits. They are little sugar treats for cockroaches laced with pesticides. Cockroach baits enable us to poison cockroaches without having to spray poison around a house. In theory, the baits can be made with any of the sugars to which roaches are attracted: fructose, glucose, maltose, sucrose, or maltotriose. In practice, glucose is always used in the United States. It is cheap, and the attraction of cockroaches to glucose is strong. The German cockroaches living in the United States are used to glucose. As much as 50 percent of their diet is composed of carbohydrates, and most of those calories come primarily from glucose. It is the same stuff we feed ourselves in huge quantities in the form of corn syrup. We bait our children to dinner with the promise of dessert using the same substance we use to bait cockroaches to death.
In those first years at Clorox, Jules realized that something had gone wrong in one of the apartments where his friend, the field entomologist Don Bieman, had placed baits. It was apartment T164. In T164, the German cockroaches weren’t dying when Don put baits out.19 They lived. He put out more baits. They still lived. When tested in the lab, cockroaches from T164 died when exposed to the poison used in roach baits at the time (hydramethylnon). The poison killed them in the lab, but not in the apartment. Don told Jules that it almost seemed like the cockroaches in the apartment were repulsed by the baits. In the lab, Jules tested the attraction of the cockroaches from T164 to the different components of the baits. The first and most obvious possibility was that the cockroaches had begun to somehow avoid pesticide in the baits. But Jules’s experiment showed that the cockroaches did not avoid the pesticide in the lab. Nor did they avoid the emulsifiers, binders, or preservatives in the baits. The only thing left to check was the sugar in the bait: glucose, aka corn syrup. It would be very surprising if the cockroaches avoided glucose, which would require avoiding a food to which cockroaches and most other animals have been attracted for millions of years—sugar. But that is exactly what had happened. The cockroaches were avoiding glucose. It wasn’t just that they weren’t attracted to it; they were repulsed. Disgusted. But they were still attracted to fructose. Perhaps, Jules thought, this particular population of German cockroaches (which would come to be called T164) had learned. Somehow, they had acquired some sort of superpower. Hell hath no fury like a clever German cockroach (except perhaps billions of clever German cockroaches).
Jules could test the idea that the cockroaches were learning. If they were, their babies—each one fleshy, pale, unprotected, and ignorant—should be attracted to the traditional baits, as should their grandbabies. The babies and grandbabies, upon birth, would not have yet had a chance to learn. Jules tested whether the babies and grandbabies were attracted to glucose. They were not. The cockroaches had not learned; they were born with an innate aversion to the sugar glucose, in particular. The only way to account for this dislike of glucose was to hypothesize that this aversion was genetic and had evolved. Jules performed simple genetic experiments to see how the aversion to glucose was inherited. He bred cockroaches averse to glucose with those still fond of it, then crossed their offspring with the parent that preferred glucose. Those crosses suggested that the gene or genes that controlled the aversion to glucose were dominant, though incompletely so.
Imagine that a family of German cockroaches moves into a big apartment building. Over time, a few cockroaches can become many more. Every six weeks, a female cockroach can produce an egg capsule containing up to forty-eight eggs. At this rate (which is fast relative to human reproduction but pretty ordinary for an insect), even if an individual female German cockroach lives only long enough to produce an egg case twice she can nonetheless give rise to ten thousand descendants in a year.20 When an exterminator places baits throughout the building and all of these thousands of cockroaches die, no evolution occurs. No particular versions of genes are favored relative to any other versions. The story is over until German cockroaches colonize the building anew and are baited again. If some of the cockroaches survive, however, and if their survival relates to a trait encoded in their genes but absent in those of the cockroaches that died, then the use of baits would actually favor the surviving cockroaches and their versions of genes. This is what Jules came to believe happened, that some version of some gene or set of genes made the T164 German cockroaches less attracted to glucose, or even repulsed by it. The T164 cockroaches had been favored, he thought, by the glucose baits and then, in their success, had rendered the baits useless.
Jules next sampled German cockroaches from around the world for glucose aversion. In many places where glucose baits had been used, from Florida to South Korea, the cockroaches had evolved aversion. And they appeared to have evolved this aversion independently in each of these places. Jules tried to repeat this finding in the lab to see whether he could actually experimentally cause evolution to occur. He gave German cockroach populations glucose baits laced with insecticide. The changes he saw in the lab resembled those occurring in the wild: over relatively few generations, glucose aversion evolved. He wrote a series of papers about his findings.21 He patented a series of roach baits based on fructose.22 He thought he might be about to launch the careers of many evolutionary biologists who could help him figure out the details of what seemed to be very rapid evolution occurring in German cockroaches.
But while pest control companies responded to Jules’s discovery by using his newly patented fructose baits, evolutionary biologists seemed to ignore the work. Jules thought he knew why: he could not explain the mechanism by which the German cockroaches evolved to be able to avoid glucose, which kinds of genes were affected, what those genes did, or even how it all happened so fast and so repeatedly. With time, though, he thought he could figure it out, and so, for years and then decades, he maintained the descendants of the German cockroaches he first studied in case one day they might be needed. Different people have different keepsakes. One man’s snow globe is another man’s perpetual cockroach colony.
While Jules waited for more insight about the German cockroaches, he went on to study other pests and their evolution. He moved to North Carolina State University in 2000, where he spent the years from 2000 to 2010 studying a population of Argentine ants (Linepithema humile) that had spread in the southeastern United States, from yard to yard and then into one building after another. He also studied the odorous house ant, Tapinoma sessile.23 For ten years, he didn’t touch a cockroach, except to continue to feed his pet colony—the descendants of the population from apartment T164—on which his biggest and largely ignored discovery was made.
In some ways, the story of the German cockroach is unique. There is no other species quite like it. But in other ways, it is just a kind of heightened example of what is happening with many of the species in our homes. Evolution can be wonderfully creative—whimsical even—in what it produces, but it also has a kind of predictability. That predictability relates to the tendency of evolution to produce convergent forms in unrelated organisms. Wings evolved independently in insects, bats, birds, and pterosaurs. Eyes evolved once in our lineage and, independently, in the lineage of squids and octopuses. In plants, trees evolved again and again, as did spines and fruits. But so did far more unusual features, such as plant seeds with tiny fruits intended for ants. The ants carry those seeds back to their nest, eat the fruit, and discard the seeds in their garbage piles, where the seeds germinate. Such ant fruits have evolved independently more than a hundred times.24 Key to predicting just which tricks evolution will repeat is an understanding of the opportunities available to species and the challenges in taking advantage of those opportunities. In our houses, the opportunity that is available is the potential to eat off our bodies, our food, and our houses themselves. The challenges have to do with arriving in our homes and surviving our assaults.
Certain circumstances lead to rapid adaptation to biocides: when the species we are trying to kill are genetically diverse (or have ways of borrowing new genes from other species); when the biocide kills nearly all (but not all) of the individuals of the species we are trying to kill; when the organisms are exposed to the biocide repeatedly (or even chronically); and when the competitors, parasites, and pathogens of the species we are trying to kill are missing. These conditions are met especially well for German cockroaches. But they are also met for nearly all of the species in our homes that we most actively try to kill and keep out. As a result, homes are one of the places in which evolution is happening most rapidly, though rarely in ways that are to our benefit.
Resistance to our pesticides has evolved among bed bugs, head lice, house flies, mosquitoes, and other common insects in houses. Natural selection can offer us great benefit, but only if we make decisions that reflect our knowledge of how it works. We don’t tend to. As a result, in our daily lives, natural selection is far more likely to prove dangerous than beneficial for us, and its dangerous gains are accumulating faster than our understanding, faster too than our ability to fight them. In short, the pests are winning so many victories that those evolutionary biologists who study resistance have been busy. They have found a great deal to do in the years since Jules discovered the glucose-averse German cockroaches, a great deal to be done even without studying those German cockroaches themselves.
The trouble was that resistance was evolving again and again, and, when it did, resistant forms replaced susceptible forms and spread. When new traits evolve on remote islands, they often stay there. Vampire finches evolved just once and never spread. Komodo dragons are confined to just five islands. But if a species evolves resistance to a biocide or other control in a home, that species can readily move to any other home in which the same control measure is being used and even those in which it isn’t. In rural environments, such spread of resistant species might be slow. But in cities, it can happen rapidly because apartments and houses are close together, because the movement of people, boxes, trucks, ships, and planes from place to place is frequent and rapid, and because the transport vehicles themselves are ever more similar to homes. Inasmuch as cities are the future, so too, then, is this ability to spread. Even though human social networks often fall apart in cities, with feelings of loneliness and isolation very much on the rise, the resistant pests are able to stay connected. Their movement is a kind of river, a river of our own making that flows through our windows and under our doors.25
Whereas resistance is quick to evolve among the species we don’t like, it is less likely to evolve among the rest of life. This is doubly problematic. The first problem it poses is the simple loss of the biodiversity around us in the world, the biodiversity on which wild ecosystems depend. A recent study found that over the last thirty years the biomass of insects in Germany had declined in wild forests by 75 percent. The jury is still out on just what caused this decline, but many scientists think that pesticide use is likely to have played a role—pesticide use on agricultural fields but also in backyards and in homes. The second problem is that the species that are most likely to die as a result of pesticides are the beneficial species in general, including, for example, pollinators and species ecologists call natural enemies, the natural enemies of the pests we are trying to control.26 The natural enemies of the pests in our homes are very often, whether you like it or not, spiders.27 If you kill the spiders in your home (and this is precisely what we do with many kinds of pesticide applications), you do so at your own expense.
As children, we learn about the old woman who swallowed a spider after swallowing a fly. That case didn’t turn out well (spoiler alert: she died). Others have turned out better. In 1959, a researcher in South Africa, J. J. Steyn, was trying to figure out how to control house flies in homes and other buildings. House flies (Musca domestica) are ancient associates of humans, having journeyed around the world with Western civilization to nearly every region in which humans live. But they can be a real problem, especially when sanitation is poor. Much more so than German cockroaches do, they vector pathogens, including many that cause diarrhea and are associated with more than five hundred thousand deaths a year. They, like German cockroaches, also rapidly evolve. By 1959, house flies in South Africa were resistant to DDT, BHC, DDD, chlordane, heptachlor, dieldrin, isodrin, prolan, dilan, lindane, malathion, parathion, diazinon, toxaphene, and pyrethrin. The flies had become, and remain, largely invincible to chemistry. But they weren’t and aren’t invincible to spiders.
J. J. Steyn gained a key insight from The Afrikaans Children’s Encyclopaedia, perhaps while reading it to his own children. The encyclopedia noted that in parts of Africa colonies of social spiders (species of the genus Stegodyphus) are intentionally brought into houses to control flies and other pests. The practice of bringing social spiders into homes to control flies appears to have first been used among the Tsonga and the Zulu. The Zulu even incorporated special sticks into the construction of their homes that made it easier for the spiders to build nests.28 The colonies of these social spiders are large, often the size of a football or a soccer ball, and easily transported from house to house by humans.
Steyn wondered whether the spiders could be used in houses again, but also outside houses and in the pens of goats and chickens, where flies were both abundant and likely to transmit disease. He tried. It wasn’t hard. In kitchens, the spider webs were suspended by a string attached to a nail. Once there, they controlled flies effectively. The spider webs were also introduced into hospitals. Again, they controlled flies effectively. Steyn repeated the experiment (boldly) in the animal house of the Plague Research Laboratory. In the laboratory, the fly population declined by 60 percent in three days. In the winter, the spiders slowed down and caught fewer flies, but there were also fewer flies to catch.
From his research, Steyn concluded, “In order to help protect humans against fly-borne diseases, it is suggested that colonies of the social spider be placed in public places like markets, restaurants, milk barns, public houses, hotel kitchens, as well as in abattoirs and dairies, and especially in kitchens and latrines on all possible premises. In cowsheds, they would also help to increase milk production.”29 He imagined a world of houses filled with giant balls of spiders, a world in which flies and the diseases they transmitted would become rare, a world in which one element of traditional Zulu or Tsonga knowledge of spiders might, again, be usefully applied.
Steyn wasn’t the only one with such a dream. In parts of Mexico lives another social spider, Mallos gregalis. This spider, too, forms large colonies (with as many as tens of thousands of individual spiders). These spiders, too, were brought into homes to eat flies, in this case by the indigenous people of Mexico.30 Just as in South Africa, this approach was part of the traditional knowledge of local people, knowledge later discovered by Western scientists. At one point, Mallos gregalis spiders were even introduced into France in an attempt to control house flies. On the first try, the plan failed when the scientist went on vacation and the person left in charge of the spiders was unable to keep them well fed. The idea of a web of a giant social spiders in your house may be off-putting, but remember that every house we have ever sampled—be it in Raleigh, San Francisco, Sweden, Australia, or Peru—has contained spiders. The question is not whether spiders are in your house controlling pests, it is whether you have enough spiders, of the right species, to do the job well.31
Spiders are not the only species that can be used in biological control in houses. Many solitary wasp species consume nothing other than one or another specific cockroach species, but they do so in a far different way than do spiders. The wasps are tiny. They do not sting. They preoccupy themselves with hunting for the egg cases of some species of cockroaches. The wasps can smell these egg cases. When they do, the mother wasps tap the egg cases to make sure they still contain live roach eggs. If they do, she then pierces the egg case with her ovipositor (egg-laying device) and lays her eggs inside. The wasp eggs hatch, devour the roaches inside the egg case, drill a hole in the egg case, and escape like young birds tipping out of the nest. In one study of homes in Texas and Louisiana, 26 percent of American cockroach egg cases were parasitized by the wasp Aprostocetus hagenowii, and another portion were parasitized by yet another wasp, Evania appendigaster.32 We did not find Evania in any houses sampled in Raleigh, but Aprostocetus hagenowii was very common. If you find an egg case in your house with a hole in it, it has likely given rise to wasps rather than to roaches. They may be in your house, flying around now, small and entirely beneficial. Several researchers have attempted to release parasitoid wasps into homes to control roaches. All of those attempts have been, in one way or another, successful (though also typically poorly documented). Nor is it just spiders and tiny wasps that can help keep our houses in order. Another research project aims to use the fungus Beauveria bassiana to control bed bugs. If sprayed on a surface in a home, the spores of Beauveria sit, waiting. When a bed bug passes, they attach to the external layer of fats on the surface of its exoskeleton. Once attached, the fungi grow through the bed bug’s exoskeleton. Once inside, the fungi proliferate in the bed bug’s body cavity and kill the bed bug by simultaneously clogging and poisoning its organs and starving the rest of its body of key nutrients.33
In our nightmares, the wasps we release to control cockroaches deposit their eggs into our bodies, and the baby wasps develop in our body cavities, eat us from the inside, and then hatch from one or another of our orifices (or make a new one). This does not happen. These wasps are small, safe, and our allies. Similarly, we imagine that the spiders in our houses might bite us. Or even consume us. They don’t, either. Spiders, too, are nearly always our allies.
Each year, tens of thousands of “spider bites” are reported around the world, and the numbers seem to be increasing. Yet spiders rarely bite humans, and nearly all of these “bites” are instead actually cases of infections due to resistant Staphylococcus bacteria (MRSA) misdiagnosed by patients and doctors alike. If you think you have a spider bite, ask a doctor to test whether you have a case of MRSA. Those odds are much higher. One of the reasons spider bites are rare is that most spiders use their venom exclusively or nearly exclusively on prey rather than in defense. For spiders, it is nearly always easier to flee than to fight. One study even attempted to find out how many pokes it took to get each of forty-three individual black widow spiders to bite artificial fingers (made out of congealed Knox gelatin). But the spiders wouldn’t bite. After one poke with an artificial finger, none of the spiders tried to bite. Nor did any of them try to bite after sixty repeated pokes. The only time in the study that a black widow bit the artificial fingers was when the fingers were used to intentionally squish the spider three times in a row. Sixty percent of the spiders squished between two artificial fingers three times in a row bit. Even then, the spiders that did bite released venom only half of the time, such that half of the bites would not have been problematic, just painful.34 Venom is costly to spiders, and they don’t want to waste it on you; they are saving it for mosquitoes and house flies.35
Our use of chemistry to kill species where we live, on the other hand, comes back to bite us again and again. Spraying pesticides in houses and backyards creates what ecologists call an enemy-free space for any pests resistant to those pesticides. Our goal should be the opposite: homes full of (rather than free of) the enemies of our pests. The use of cockroach baits, for example, was supposed to be a solution to this problem. The pesticides would be consumed by the pests, but not by their predators. But then the cockroaches evolved a way around even this human innovation. Just how they evolved remained a mystery until 2011. By that point, Jules Silverman had begun to shift the work he was doing in the lab. He stopped working on cockroaches and ants and was beginning to spend most of his research time on aquatic insects. He converted his lab into a series of giant tanks filled with caddisflies and algae. He started teaching a class on aquatic insects. He was sinking, waders first, into a new phase of his life. But Jules kept feeding the cockroaches, and he continued to search the literature for ways to help solve his riddle, the riddle of the resistant cockroaches. He would soon have company in this quest.
Jules works in an aging building at North Carolina State University, a building in which air conditioners and heaters dangle in windows. The air conditioners are not for the people in the rooms but instead are used to keep comfortable the insects under study by the university’s entomologists, which include Jules’s cockroaches. Because the insects being studied tend to be household pests, they need to be kept in conditions similar to those found in a modern house, with constant temperature and relatively constant humidity. For the insects the climate is controlled. Each entomologist keeps a different creature. In the lab of Wes Watson, a veterinary entomologist, one can find the flies that live on the eyes of cows or the beetles that wriggle through their dung. In the lab of Michael Reiskind, an expert on the ecology of mosquitoes, blood-fed female mosquitoes lift off with each shake of the walls (the walls do shake, especially when a train goes by) and then settle back down. But the lab in which the most kinds of pests can be found is that of Coby Schal, an expert on the ways in which household pests communicate with each other. In Coby’s lab, bed bugs cling to blood-filled membranes and a half dozen species of cockroaches stumble, in great densities, over one another’s bodies.
Like Jules’s, Coby Schal’s work includes the study of cockroaches, especially German cockroaches. Coby is a chemical ecologist: he sees nature as a function of the chemical signals organisms use to communicate with each other. More specifically, he is an expert in the chemistry of cockroaches and how they communicate with each other. He has discovered, among many other things, a pheromone used by wild female cockroaches to attract males. He can put this pheromone out in a field (or even hold it up in his hand) and male cockroaches come flying toward him, only to be disappointed.36 Jules knew of Coby’s work long before the two ever became colleagues. He cited one of Coby’s papers in his own first paper on cockroaches. But even once they were both at the same university, the two didn’t work together on cockroaches. They teamed up to study Argentine ants, and odorous house ants, but not German cockroaches. Maybe they were just both busy with other collaborations. Maybe Jules didn’t think Coby’s skills were quite what he needed to resolve the questions he was most interested in. For some mix of reasons, no cockroach collaboration materialized.
And then a new postdoctoral researcher from Japan, Ayako Wada-Katsumata, arrived in the department in 2009. Postdoctoral researchers very often have skills their bosses lack. They also have more time to do research and so can, through their work, build bridges where none existed before. Such was the case with Wada-Katsumata. She had the skills that bridged Coby’s and Jules’s work and, in doing so, ushered forth what Jules regards as one of the most important discoveries of his career.
Wada-Katsumata’s special skill is measuring how the brains of insects such as cockroaches respond to compounds they taste or smell. Before coming to North Carolina State University, Wada-Katsumata considered whether sharing food triggers chemicals associated with pleasure in the brains of ants. (It does.) She also studied the sensory experiences of cockroaches during courtship and sex. During courtship, male and female German cockroaches find each other in the dark. The female cockroach produces a chemical signal that becomes airborne and drifts through a house and attracts male roaches to her. The chemical drifts out of kitchen cupboards and up from beneath cabinets. It drifts around corners and up the stairs. Even when the lights are out, the male can find the female by chasing her odor.37 The male and female then make contact, and when they do, the male detects other chemicals produced on the female’s body. In response, he offers up a nuptial gift, a package of sugars and good odors, a kind of sexual candy filled with sugar and fat. Depending on her satisfaction with this gift (which she eats regardless), she decides whether or not to mate. When Wada-Katsumata began her work on cockroaches, the composition of the nuptial gift of male roaches was known, but the response the gift triggered in the brains of female roaches was not. To figure out the answer, Wada-Katsumata wired the taste neurons of German cockroaches, neurons located on tongue-like sensilla, to a computer and then offered both females and males different kinds of gifts. In this particular experiment, she was playing the role of the male cockroach. When she did, she found that the male’s gift was perceived as a tasty food by both the male and the female, but that the food stimulated the female’s neurons more strongly than it did the male’s. If a male cockroach grew despondent and lonely, he could eat his own “gift” and enjoy it, but not nearly as much as a female would.
In North Carolina, Wada-Katsumata would consider almost the opposite of what she was working on in Japan. Rather than study the response of German cockroaches to something they sought out, sex, she’d study the response of the T164 cockroaches to something they avoided, glucose. Jules believed and Coby, through their discussions, had also come to suspect, the T164 cockroaches had evolved a way of responding aversively to the taste of glucose. One outlandish possibility was that natural selection had favored T164 cockroaches in which glucose triggered the “bitter” neurons on sensilla rather than the “sweet” ones. Perhaps they touched the glucose with their sensilla and their brains shouted “Bitter! Walk away!” It was already known that the sweet taste receptors of ordinary German cockroaches (what scientists call “wild type” cockroaches) respond to both glucose and fructose. But was the same still true of the T164 cockroaches? Wada-Katsumata would try to figure it out. Like a cockroach mind reader, she would test what the cockroaches perceived.
The task would consume most of her working hours. Morning after morning, she ate breakfast, traveled to the lab, gathered up a cockroach, and then corralled it into a tiny cone put on so that the cockroach’s head stuck out the small end of the cone and its bulbous, swollen body protruded out the other.
Once the cockroach was set up in its cone, Ayako looked through a microscope at the hair-like sensilla on its mouth. She connected one end of an electrode to a single sensillum. The other end of each electrode ran to her computer. The electrode connected to the sensillum was surrounded by a narrow tube containing water and glucose (or whatever else she might want to offer the cockroaches in this taste test). Depending on the amplitude and frequency of the impulse on her computer screen, Wada-Katsumata interpreted whether the food she had given the cockroach, be it fructose, glucose, or anything else, triggered “sweet” neurons or “bitter” neurons on the sensillum. If she saw a fast pulse on her screen, she knew the “bitter” neurons were triggered; the cockroach perceived bitter. If she saw a slightly slower and larger-amplitude pulse, she knew that the “sweet” neurons were triggered; the cockroach perceived sweet. It was an elaborate process, one that Wada-Katsumata repeated for five sensilla from each of two thousand roaches—half of them from the T164 population, half of them wild type.
The work took more than three years. Over these three years, Wada-Katsumata sat eye to eye with these cockroach heads, testing them. They looked at her. She gave them sweets. They responded to those sweets with tiny impulses that showed on her screen. She saved the resulting data in the computer. She backed up the data. She did this both for German cockroaches that were glucose-averse (Jules’s T164 German cockroaches) and for normal German cockroaches that ran higgledy-piggledy toward the stuff. It took a full day to test each individual cockroach, sensillum by sensillum. The experiments required patience, persistence, and then, when those were both all gone, something a little more. And all of this because Jules and Coby, and now Wada-Katsumata, thought that the key to understanding population T164 might have to do with what happens in their brains when they taste glucose.
Wada-Katsumata’s results slowly accumulated. There was no key moment. Eventually, the answer was finally so clear no more testing was necessary. The T164 cockroaches and the wild type cockroaches both perceived fructose as sweet in the same way that the cockroaches she had studied in Japan perceived each other’s sex signals as sweet. Fructose triggered their sweet neurons. The wild cockroaches also perceived glucose as sweet. All of this was as expected. But—and here was the key—the cockroaches Jules had dragged with him city to city—his tether to his former life, the T164 specimens—perceived glucose as bitter.38
How could this be? The only possible interpretation is that the original cockroach baits in apartment T164, baited with glucose, were so deadly that most—but not all—roaches died. And some of the roaches that didn’t die were those that avoided the baits entirely because they had a version of a gene or genes that led them to perceive the bait itself as bitter. This needed to happen only once. From that single event, all of the T164 German cockroaches may well have derived. Time has added nuance to this story, though ambiguities remain. For example, Wada-Katsumata has shown that not only were the surviving cockroaches averse to glucose but also, in regions where baits were originally baited with fructose rather than glucose, the roaches evolved to perceive the fructose as bitter instead. This means that the evolution of the roaches is predictable. Evolution in light of our actions is predictable. What is not yet understood is which specific versions of which specific genes were favored so as to lead the T164 cockroaches to perceive glucose as bitter.
Wada-Katsumata is back in the lab. Jules has charged her with taking care of his cherished cockroaches from apartment T164; he has passed on the care of their line. He is pondering retirement and Wada-Katsumata’s career is just beginning. They would be her legacy now. With these cockroaches, she is studying how the evolution of an aversion to sugars affects the sex lives of roaches. It is an integration of the work she did before she came to North Carolina State University and her work with Coby and Jules. The long answer with all of its context and contingent details has yet to emerge because the science is slow and hard and a clear picture could well take her whole career to emerge. But the short answer is that the roaches that dislike glucose are less able to mate. Males try to attract females, but their sweet chemical telegram contains glucose, so rather than being sweet, sexually sweet, it is bitter. Consequently, the female often skips the sex and moves on. Who can blame her? Because female cockroaches are more likely to walk away from sex with bitter males, for the male cockroaches in your house a trade-off exists between being sexy and surviving. In theory, this means that when you use cockroach poisons laced with glucose, you are favoring the lineages of cockroaches less able to get it on and so less able to fertilize enormous indoor cockroach populations. In practice, though, a less-than-fully-sexy male cockroach is still sexy enough to beget millions of descendants.
It might seem that the story of the German cockroaches of population T164 sheds light only on the evolution of cockroaches themselves or on the ways in which a clever and persistent scientist can reveal what seemed to be unknowable. But just as military specialists study the battles of the past to prepare for the future, we might consider our battle with the German cockroach in contemplating our own evolutionary future.
Evolutionary biologists spend very little time writing about and predicting the distant future. It isn’t that they are shy about making predictions but instead, I suspect, it is because the evolutionary future is entirely contingent on the fate of our species. Evolutionary biologists know that every species eventually goes extinct. We will too. They know that in our absence evolution will continue, as it long has.39 It will be punctuated by the occasional disaster, as it long has been, and yet it will tend inevitably toward more diversity, more kinds of life, as has happened after every major extinction or change in the evolutionary past. In our absence, the future will unfold according to the general rules of evolutionary biology. There is horror in such a view of life, the horror of the end of our kind, but there is also a kind of solace in knowing life will go on without us and will offer up forms of existence we have yet to imagine (and won’t be around to see either).
Thinking about what happens while we’re still around is trickier. So much depends on the decisions we make and the innovations we offer up to the world. We now control much of the evolution occurring on Earth, albeit unwittingly and with sloppy orchestration. In light of this, the easiest outcome to consider is what will happen if we continue to make the same sorts of choices we have made over the last hundred years. These choices are, in turn, the same sorts of choices we have made over the last thousand, ten thousand, and even twenty thousand years, choices to kill what is problematic or aesthetically unpleasant and visible with ever more powerful weapons.
This is a future that is easy to imagine. It is a future in which the use of novel chemicals as weapons favors the evolution of ever more behaviorally and chemically defended pathogens and pests and leaves far behind—if they are left at all—the species that might benefit us. The pests will be resistant, but the rest of life, the rest of biodiversity, won’t be. We will unknowingly trade a richness of wild species—of butterflies, bees, ants, moths, and the like—for the few resistant life-forms. The exoskeletons of those enduring life-forms will be coated with barriers that prevent toxins from entering their bodies. Their individual cells will have transporters that prevent toxins from being moved in (or special fat bodies where toxins that have moved in can be stored safely). Like the cockroaches, they might also be ascetic, forgoing the diets and maybe even the sex pheromones with which we bait them to their deaths. It is already happening, but will accelerate and become more extreme, and more global. The more homogenous and climate controlled we make our spaces, the easier we make indoor life for ourselves, and the easier indoor life will be for them too.
And whereas what evolved in the Galapagos Islands, where Charles Darwin most clearly saw the process of natural selection and its result, evolution, was animals without fear of humans, what is evolving around us is the opposite: a miniature army that knows just how to avoid us and our assaults. Indoor pests will continue to be nocturnal. They will specialize in whatever hours we do not occupy, the hours in which we fail to pay attention (we kill pests when we notice them). To some extent, this has already happened. Bed bugs evolved from bat bugs sometime when humans lived in caves. Bat bugs are diurnal; they eat at bats when bats are sleeping. Bed bugs, on the other hand, have evolved to be nocturnal, so they can eat at us when we are sleeping. So too have many cockroaches and rats turned nocturnal. Animals will also evolve to sneak through ever smaller cracks. The more we seal up our buildings, the smaller these organisms will get. The most obvious future is one in which the thousands of species of animals we now find in homes, each with an interesting story and most with no negative effect on humans whatsoever, will be gone and in their place we will be surrounded by the consequences of our actions, thousands of tiny, resistant, evasive German cockroaches, bed bugs, lice, house flies, and fleas. We will be surrounded by their diminutive army, an army that skitters away from us on its many, many legs when we turn on the lights and then, as soon as we disappear or turn the lights back off, regroups and reclaims.