Why Bumblebees Love Cats and Other Beautiful Relationships

On the wonders and benefits of natural relationships and what happens when humans meddle with the delicate balance between species.

Stefano Mancuso | The Nation of Plants | March 2021 | 3,311 words (19 minutes)

I am sure that many of the erudite readers of this little book know On the Origin of Species by Charles Darwin inside and out. If there is someone who still has this gap in their education, you are urged to fill it without any further delay. Darwin’s book is fundamental for understanding how life works. And it is surprising to think how this book, which literally changed the history of the world, is actually only a summary of the countless observations that Darwin gathered for decades throughout the scientific disciplines and throughout the world in support of his theory of the evolution of living species. His plan, in fact, was to write a colossal and minutely detailed work that was meant to report all the fruits of his decades of research. It would be a work invulnerable to any and all criticism.

As is well known, things did not work out that way. Alfred Russel Wallace’s announcement that he had arrived at Darwin’s same conclusions regarding evolution induced Darwin to change his plans and summarize in Origin his most brilliant and most evidentially supported deductions, leaving the rest of the material for subsequent elaboration. Nevertheless, the enormous corpus that he was working on did not go to waste. On the contrary, the first two chapters of his magnum opus, which was supposed to be entitled simply Natural Selection, became the two volumes of The Variation of Animals and Plants Under Domestication, and much of the rest of the material was readapted in the elaboration of his later works. In any event,
in the third chapter of On the Origin of Species, dedicated to the famous “struggle for existence” that is the dominant motif of the whole book, Darwin tells a marvelous story of relationships. This story is essential for understanding both the bonds between living beings and how difficult it is to imagine the consequences of intervening in those relationships.

Darwin writes: what animals could you imagine to be more distant from one another than a cat and a bumblebee? Yet the ties that bind these two animals, though at first glance nonexistent, are on the contrary so strict that were they to be modified, the consequences would be so numerous and profound as to be unimaginable. Mice, argues Darwin, are among the principal enemies of bumblebees. They eat their larvae and destroy their nests. On the other hand, as everyone knows, mice are the favorite prey of cats. One consequence of this is that, in proximity to those villages with the most cats, one finds fewer mice and more bumblebees. So far so clear? Good, let’s go on.

Bumblebees are the primary pollinators of many vegetable species, and it is common knowledge that the greater the amount and the quality of pollination the greater the number of seeds produced by the plants. The number and the quality of seeds determines the greater or lesser presence of insects, which, as is well known, are the principal nutriment of numerous bird populations. We could go on like this, adding one group of living species to another, for hours on end: bacteria, fungi, cereals, reptiles, orchids, would succeed one another without pause, one by one, until we ran out of breath, like in those nursery rhymes that connect one event to another without interruption. The ecological relationships that Darwin brings to our attention tell us of a world of bonds much more complex and ungraspable than had ever previously been supposed. Relationships so complex as to connect everything to everything in a single network of the living.

There is a famous story along these lines told for the first time by the German biologists Ernst Haeckel and Carl Vogt. As the story goes, the fortunes of England would seem to depend on cats. By nourishing themselves on mice, cats increase the chances of survival of bumblebees, which, in turn, pollinate shamrocks, which then nourish the beef cows that provide the meat to nourish British sailors, thus permitting the British navy—which, as we all know, is the mainstay of the empire—to develop all of its power. T. H. Huxley, expanding on the joke, added that the true force of the empire was not cats but the perseverant love of English spinsters for cats, which kept the cat population so high. In any event, underlying the joke is the simple truth that all living species are connected to one another in some way or other by relationships, visible or hidden, and that acting directly on one species, or simply altering its environment, can have totally unexpected consequences. Darwin tells us that trying to imagine the final consequences of any alteration in these relationships would be as “hopeless” as throwing up a handful of sawdust on a windy day and trying to predict where each particle would land.9 History is full of such attempts, almost always gone wrong, to modify the presence or the activities of single species.

T. H. Huxley, expanding on the joke, added that the true force of the empire was not cats but the perseverant love of English spinsters for cats, which kept the cat population so high.

Let’s take as an example the affair of the color red. When Cortés and his conquistadores first entered the Aztec capital of Tenochtitlán (present- day Mexico City), they found a very rich and very populous city (in Europe at the time only Naples, Paris, and Constantinople had larger populations). In the enormous market square, a quantity of goods never seen before, many of them of great value, were just waiting to be exported to European markets. Among them were bales of finely woven cotton and delicate yarns of an amazing carmine red. The dye used by the Aztecs to produce this incredible tone of red was obtained from a tiny insect, the cochineal, that lives on cactus plants (various species belonging to the genus Opuntia, the prickly pear). The color was so beautiful and precious that states under Aztec domination were required to furnish annually to the emperor a certain number of sacks full of cochineals as tribute. A fine brilliant carmine dye was, and still is, obtained from the dried bodies of these insects.

The production of this dye remained, for almost two and a half centuries, a monopoly of Spain, which guarded the secret jealously and made it into a widespread and highly profitable commerce in Europe. The Spanish sold their dye to whoever could afford it, but above all to the English, who soon became its most enthusiastic and passionate buyers. Enamored of Spanish carmine, which they used to color their military uniforms (their famous red coats), the English found a way to buy it at a high price even during their frequent wars against Spain, in which those very uniforms were used. As Italians say, the heart will not be ruled. That special hue of carmine provided by the Spanish dyes was essential for the British army. Any other red would have made their coats less red, demeaning the glorious nobility of the uniform. After all, what kind of image would they have projected in battle with faded uniforms? Their enemies would have died laughing; and that was no way to win a war.

Enamored of Spanish carmine, which they used to color their military uniforms (their famous red coats), the English found a way to buy it at a high price even during their frequent wars against Spain, in which those very uniforms were used.

For the next 250 years, despite the best efforts of the English to free themselves from this commercial yoke, the secret of that prodigious dye remained unknown to all but a select fortunate few of Spanish producers. But no production secret can stay that way forever, and so in the closing years of the eighteenth century, British spies succeeded in spiriting away the tightly kept formula: in order to obtain the longed-for carmine, you needed cochineals, and to get cochineals you had to have prickly pears. With the right information in hand, all that remained was to find the right place to begin production. There was no shortage of candidates; the empire was enormous and spread over all the continents. The choice fell on the fortunate Australia. Prickly pears had never grown there, but its climate was perfect for their rapid growth, so both prickly pears and cochineals were imported.

The results were not long in coming. The cochineals died immediately on arrival in Australia, while the prickly pears, useless at this point, were abandoned to their Australian destiny. A destiny of conquerors. Unlike the cochineals, the prickly pears found the Australian environment ideal for their dispersion. With no natural enemies or obstacles and with lots of birds to disperse their seeds, in just a few years the plant spread throughout a vast territory. Having arrived in Australia from Brazil in 1788, the prickly pear was dispersed over an estimated seventy-three million acres, and its expansion did not stop there. It went on conquering new territories at an astounding rate of 1.2 million acres per year. Thus, large amounts of cultivated land, farms, pasture, and agricultural areas of Queensland and New South Wales were invaded by prickly pears, driving away farmers and impeding any kind of productive activity. The problem soon became very serious, forcing the authorities, starting in the second half of the nineteenth century, to look for possible solutions.


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In 1901, the government of New South Wales offered £5,000 to anyone who came up with an idea to block the invasion. In 1907, even though the reward had been doubled, it seemed that no one was able to provide an adequate solution. Naturally, there was no shortage of far-fetched proposals. Many people came forward with stratagems that were, let’s say, radical. Among them: increase the number of rabbits as predators of the prickly pear, another interesting story of species introduction gone awry. Or, another gem, evacuate an enormous area of land and use airplanes to spray mustard gas (the gas widely used in World War I) to exterminate the animal population, which was responsible for the dispersal of prickly pear seeds. Fortunately, neither of these proposals was taken into consideration, and for decades the only weapon against the devastating advance of the species was to cut down and burn the plants.

Then, in 1926, a solution was finally found: an Argentine lepidopteran (moth) known as Cactoblastis cactorum, a parasite of various species of Opuntia. By nourishing themselves on cladodes (as the modified leaves of prickly pears are called) the moth larvae managed to debilitate the prickly peril in many parts of Australia. This stratagem enjoyed an extraordinary and unexpected success. In a short time, except in the cooler parts of Australia, where the moth spread less effectively, the prickly pear menace was eliminated.

So it all worked out? In part. Although the introduction of the Cactoblastis in Australia is often cited as a successful operation, so much so that the community of Boonarga, just east of the city of Chincilla in Queensland, even dedicated its Cactoblastis Memorial Hall to the moth. Nature always wants the last word. Over time, populations of prickly pears resistant to the parasite evolved in Australia, and this is a first, though not fatal, complication that will, however, require a more careful control of the cactus population in the future. But the second and more important difficulty is that the Australian success in the use of the lepidopteran induced many other nations with analogous prickly pear problems to go down the same road, with totally unexpected results. As Darwin advised us, trying to predict what will happen in a situation like this is like trying to predict where a piece of sawdust will land on a windy day.

In the 1960s the Cactoblastis was introduced to the Caribbean islands of Montserrat and Antigua as a control agent of the local cactus populations. In Australia, the sawdust fell in the right spot, but in Central America, it didn’t. The moth, in fact, using all kinds of carriers, spread quickly to Puerto Rico, Barbados, the Cayman Islands, Cuba, Haiti, and the Dominican Republic. Through the importation of prickly pears from the Dominican Republic, it arrived for the first time in Florida in 1989, and from there it began to spread at a velocity of over a hundred miles per year along the coast of the Gulf of Mexico. During its expansion, by now completely out of control, this parasite has endangered many cactus populations in the United States and the Caribbean, threatening entire ecosystems, some of them unique. A classic example is the attack on the prickly pear on the Bahamian island of San Salvador, one of the main sources of food for the only extant populations of Cyclura iguanas.

And as if all this were not enough, hurricanes, involuntary transport, and trade have recently transported the Cactoblastis to Mexico, where it has been sighted for the first time on the island of Mujeres, just off the Yucatan peninsula. In Mexico, unlike in Australia, the prickly pear is a vital plant. It even appears in the national emblem and on the flag. Its fruit and cladodes are a staple food for the population. Prickly pears are used to feed livestock in periods of drought, and some species of Opuntia are still used by the cochineal dye industry. If the Cactoblastis were to spread to the Mexico mainland, the damage would be enormous.

But no other natural disaster provoked by humans following rash decisions based on inadequate knowledge of natural relationships will ever be able to rival what Mao Tse-Tung accomplished in the late 1950s. Between 1958 and 1962, the Chinese Communist Party led an economic and social movement in the whole country that came to be known as the Great Leap Forward. This was an enormous collective endeavor meant to transform China in just a few years from an agricultural nation into a great industrial power. The movement’s results, unfortunately, fell dramatically short of what had been hoped. The reforms through which the party intended to effect this radical national change involved every area of Chinese life, and some of them had devastating effects for the country.

In 1958, Mao was rightly convinced that some of the scourges that had plagued the Chinese for centuries had to be eradicated immediately and in a radical fashion. Keep in mind that when the Communists took power in the autumn of 1949, they found themselves governing a nation gravely distressed by a soaring incidence of infectious diseases: plague, cholera, measles, tuberculosis, polio, and malaria were endemic in most of the country. Cholera epidemics were very frequent, and the infant mortality rate ran as high as 30 percent.10

The creation of a national health service and a massive vaccination campaign against plague and measles were the first, meritorious, actions undertaken to improve the situation. Water purification and sewage treatment infrastructure was installed throughout the country, and imitating what had been done previously in the Soviet Union, health care personnel were trained and sent into rural areas to serve as proper health care administrators, educating the population in basic health and hygiene practices and treating diseases with all available resources. But, obviously this wasn’t enough; the diffusion of carriers that spread disease had to be curtailed: mosquitoes, responsible for malaria; rats, spreaders of plague; and, finally, flies had to be exterminated. These three scourges from which China had to be liberated were soon joined by a fourth: sparrows, which by eating fruit and rice cultivated laboriously in the fields were one of the most terrible enemies of the people. Chinese scientists had calculated that each sparrow ate ten pounds of grain per year. So for every million sparrows killed, food for 60,000 people would be saved.

This information was the basis for the “Four Pests Campaign,” and sparrows were public enemy number one. Today, any proposal for ecosystem modification as radical as this call to eliminate four species from a territory as vast as China would, obviously, be considered ill-considered. But in 1958, lots of people thought it seemed like a good idea. So the party’s campaign to recruit the citizenry to combat these four pests was begun. Millions of posters were printed up illustrating the necessary eradication and the means to implement it.

Chinese scientists had calculated that each sparrow ate ten pounds of grain per year. So for every million sparrows killed, food for 60,000 people would be saved.

For the battle against sparrows, the people were told to give no quarter and to use all available means. One of the directives was to frighten the sparrows with noise, produced in any way possible, so they would be forced to fly constantly without ever coming to rest, until they fell to the ground exhausted. Pans, casseroles, gongs, rifles, trumpets, horns, plates, tambourines—any source of noise was put to use. Here is a description of what happened by a Russian observer, Mikhail A. Klochko,11 who was working as a consultant in Beijing when the four pests campaign was launched:

I was awakened early in the morning by the sound of a woman screaming. Rushing over to the window, I saw a young woman running back and forth on the roof of a nearby building, frenetically shaking a bamboo pole with a large sheet tied to it. Suddenly, the woman stopped yelling, apparently to catch her breath, but an instant later, down at the end of the street, a drum started beating, and the woman went back to her blood-curdling screams and the mad shaking of her peculiar banner. This went on for several minutes. Then the drums stopped beating and the woman fell silent. I then realized that, on all the upper floors of my hotel, women dressed in white were waving sheets and towels that were meant to prevent sparrows from landing on the building. This was the opening of the Great Sparrow campaign. All day long I heard drums, gunshots, and screams and saw fluttering sheets, but never at any time did I see a single sparrow. I cannot say whether the poor birds had perceived the mortal danger and flown off in advance to safer terrain, or if there had never been any sparrows in that place. But the battle went on without abatement until noon, with the entire staff of the hotel mobilized and participating: porters, front office managers, interpreters, chambermaids and all the rest.

Although Klochko’s account makes it seem that all this activity was not very effective, the actual results were, unfortunately, devastatingly successful. The government acclaimed the schools, working groups, and governmental agencies that achieved the best results in terms of number of pests killed. The estimates provided by the Chinese government, totally unreliable for their enormity, indicated a billion and a half rats and a billion sparrows killed. Even though they are enormously exaggerated, these figures nevertheless tell us of a massacre whose dramatic consequences would soon be evident. Sparrows, in fact, do not feed exclusively on hulled grains. On the contrary, their main food supply are insects.

In 1959, Mao, realizing his mistake, replaced the sparrows as a target pest with beetles, but the damage had already been done. The almost total lack in China not only of sparrows (which had to be reintroduced from the USSR) but of practically all other birds led to an immeasurable increase in the insect population. The number of locusts began to increase exponentially, and immense swarms of insects making their way through the fields of China destroyed most of the crops. From 1959 to 1961, a series of ill-starred events partially related to natural disasters and partly caused by the mistaken reforms of the Great Leap Forward (the idea to exterminate the sparrows being one of the worst), led to three years of famine so harsh that it caused the deaths of an estimated 20 to 40 million people.

Playing with something whose working mechanisms are not well known is clearly dangerous. The consequences can be completely unpredictable. The strength of ecological communities is one of the engines of life on Earth. At every level, from the microscopic to the macroscopic, it is these communities, understood
as relationships among the living, that allow life to persist.

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Excerpted from The Nation of Plants by Stefano Mancuso, translated by Gregory Conti. Soon to be published by Other Press.

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9. R. C. Stauffer, ed., Charles Darwin’s Natural Selection; being the second part of his big species book written from 1856 to 1858 (Cambridge: Cambridge University Press, 1975).

10. David M. Lampton, “Public Health and Politics in China’s Past Two Decades,” Health Services Reports 87, no. 10 (Dec. 1972): 895–904.

11. Mikhail A. Klochko, Soviet Scientist in Red China (London: Hollis & Carter, 1964).